Nanovoided polymers having shaped voids

ABSTRACT

An example device includes a nanovoided polymer element, a first electrode, and a second electrode. The nanovoided polymer element may be located at least in part between the first electrode and the second electrode. In some examples, the nanovoided polymer element may include anisotropic voids. In some examples, anisotropic voids may be elongated along one or more directions. In some examples, the anisotropic voids are configured so that a polymer wall thickness between neighboring voids is generally uniform. Example devices may include a spatially addressable electroactive device, such as an actuator or a sensor, and/or may include an optical element. A nanovoided polymer layer may include one or more polymer components, such as an electroactive polymer.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 62/777,825, filed Dec. 11, 2018, the disclosure of which is incorporated, in its entirety, by this reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate a number of exemplary embodiments and are a part of the specification. Together with the following description, these drawings demonstrate and explain various principles of the present disclosure.

FIGS. 1A-1C depict an NVP element with spherical voids, showing variations in wall thickness.

FIG. 2A-2D depict a portion of an NVP undergoing compression.

FIG. 3A-3F depict an NVP with improved wall thickness uniformity.

FIGS. 4A-4B depict a buckling deformation in an isotropic NVP.

FIGS. 5A-5C depict an anisotropic NVP, in accordance with some embodiments.

FIGS. 6A-6C also depict an anisotropic NVP having improved compression properties, in accordance with some embodiments.

FIG. 7A-7C show anisotropic NVPs having different void fractions, in accordance with some embodiments.

FIGS. 8A-8B depict voltage-actuation curves of NVPs showing improved compression properties, in accordance with some embodiments.

FIGS. 9A-9C and 10A-10B depict the relatively insignificant effect of polydisperse voids on the compression properties of NVPs, in accordance with some embodiments.

FIG. 11A-11B depict exemplary NVP elements having electrodes disposed thereon, in accordance with some embodiments.

FIGS. 12A-12C depict exemplary actuators in accordance with some embodiments.

FIG. 13 depicts an exemplary electrode arrangement, in accordance with some embodiments.

FIG. 14 shows a deposition apparatus which may be used to deposit a nanovoided polymer element, along with any additional layers.

FIG. 15 shows a voided polymer material including a periodic array of voids.

FIG. 16 shows an example method of operation of an NVP element.

FIGS. 17 and 18 illustrate example methods of forming a voided polymer material.

FIG. 19 illustrates an example system.

FIG. 20 is an illustration of exemplary augmented-reality glasses that may be used in connection with embodiments of this disclosure.

FIG. 21 is an illustration of an exemplary virtual-reality headset that may be used in connection with embodiments of this disclosure.

FIG. 22 is an illustration of exemplary haptic devices that may be used in connection with embodiments of this disclosure.

FIG. 23 is an illustration of an exemplary virtual-reality environment according to embodiments of this disclosure.

FIG. 24 is an illustration of an exemplary augmented-reality environment according to embodiments of this disclosure.

Throughout the drawings, identical reference characters and descriptions indicate similar, but not necessarily identical, elements. While the exemplary embodiments described herein are susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, the exemplary embodiments described herein are not intended to be limited to the particular forms disclosed. Rather, the present disclosure covers all modifications, equivalents, and alternatives falling within the scope of the appended claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Polymer materials may be incorporated into a variety of different optic and electro-optic architectures, including active and passive optics and electroactive devices. Electroactive polymer (EAP) materials, for instance, may change their shape under the influence of an electric field. EAP materials have been investigated for use in various technologies, including actuation, sensing, and/or energy harvesting. Lightweight and conformable, electroactive polymers may be incorporated into wearable devices (such as haptic devices) and are attractive candidates for emerging technologies, including virtual reality/augmented reality devices where a comfortable, adjustable form factor is desired.

Virtual reality (VR) and augmented reality (AR) eyewear devices or headsets, for instance, may enable users to experience events, such as interactions with people in a computer-generated simulation of a three-dimensional world or viewing data superimposed on a real-world view. VR/AR eyewear devices and headsets may also be used for purposes other than recreation. For example, governments may use such devices for military training, medical professionals may use such devices to simulate surgery, and engineers may use such devices as design visualization aids.

These and other applications may leverage one or more characteristics of thin film polymer materials, including their electrical, mechanical, and/or optical properties. There is a need, for example, for improved actuators, sensors, and optical elements, along with associated methods for applications in AR and VR devices.

The present disclosure is generally directed to nanovoided polymers (NVP), electroactive NVP elements, methods of preparing NVP elements, and devices, methods, and systems including electroactive materials, such as NVP elements. Embodiments of the instant disclosure may include nanovoided polymers, layers thereof, electroactive and/or sensor elements including such nanovoided polymers, applications of nanovoided polymers in devices such as actuators, optical elements (which may include actuators), sensors, and combinations thereof, methods of fabrication of any of the above, and methods of operating any such device.

In some examples described herein, the term voided polymer may refer to a material including a polymer matrix and including voids within the polymer matrix. In some examples, the term “void” may refer to a volume of fluid material within the polymer matrix. For example, a void may include a gas (such as air, nitrogen, an inert gas, or the like), a liquid, or other fluid medium, such as a foam. Voids may include nanovoids, which may include voids having at least one interior dimension (such as a diameter or other analogous interior dimension) that is less than approximately 1 micron. A polymer matrix may include one or more polymer components, and may include other non-polymer components, such as nanoparticles and the like.

As will be described in greater detail below, examples of the instant disclosure include electroactive devices, such as NVP elements, actuators, sensors, and optical elements, having, for example, improved electrical and/or mechanical properties, such as improved electrical control of actuation and/or improved spatial resolution of sensing. Features from any of the embodiments described herein may be used in combination with one another in accordance with the general principles described herein.

In some examples, a method of fabricating a nanovoided polymer includes depositing a precursor composition onto a substrate. The substrate may include one or more components and/or layers subsequently used in a device, such as a polymer layer, electrode, or the like. In some examples, the fabricated nanovoided polymer may be released from the substrate before further processing. The precursor composition may include at least one polymerizable species, such as one or more monomer molecular species, or one or more oligomer molecular species. The precursor composition may also include a liquid in which the monomer dissolves and/or a liquid immiscible with the monomer (or which does not dissolve the monomer, for example, if the monomer is solid, and which in some examples may not mix with any solvent used to dissolve the monomer). In some examples described herein, a polymerizable species may be referred to as a monomer for conciseness, though examples are not limited to the use of monomers, as other polymerizable species may be used, such as oligomers. In some examples, the term oligomers may include dimers, trimers, and the like.

Nanovoided polymers may include new classes of materials, for example, materials in which a polymer matrix includes fluid-filled voids, such as gas-filed voids. In some examples, voids may include nanovoids that may have an average diameter (or analogous dimension) between approximately 10 nm and approximately 1000 nm. The introduction of nanovoids into the bulk polymer film provides an added degree of material property tunability, for example, in terms of overall macroscopic properties, including electrical, mechanical, thermal, diffusive, and/or chemical properties.

Voids may be formed in a material from the inclusion of a fluid (such as a gas or liquid), and the fluid may naturally form spherical shapes (e.g., spherical droplets) to minimize surface energy. A material, such as an emulsion, including spherical droplets may be used to form a voided polymer (e.g., a nanovoided polymer) including spherical voids. However, anisotropic voids in polymers may provide material that are favorable for various applications, for example, where the material is compressed, and may also modify how the material interacts with light. An anisotropic NVP may include nanovoids elongated in at least one direction, such as a direction approximately perpendicular to a direction of an applied electrical field (when a potential is applied between electrodes), or perpendicular to a direction of compression (e.g., a compression that may result from electrostriction, or a compression that may be detected in a sensor device). Voids having an average diameter (or analogous dimension) of less than approximately 1 micron (1000 nm) may be termed nanovoids.

The following will provide, with reference to FIGS. 1-24, detailed descriptions of, for example, voided polymer films, their preparation, and applications. FIGS. 1A-2D illustrate example nanovoided polymer elements, wall thickness aspects, and example buckling deformations. FIGS. 3A-4B illustrate NVPS having improved wall thickness uniformity, and behavior under compression. FIGS. 5A-6C depict example anisotropic NVPs with improved compression properties. FIGS. 7A-7C illustrate various anisotropic NVPs having different void fractions. FIGS. 8A-8B depict improved compression properties of example NVPs. FIGS. 9A-9C and FIGS. 10A-10B depict the relatively insignificant effect of polydisperse voids on the compression properties of NVPs. FIG. 11A-13 depict exemplary NVP elements having electrodes disposed thereon. FIG. 14 shows an example deposition apparatus, and FIG. 15 shows a voided polymer material including a periodic array of voids. FIGS. 16-18 illustrate example methods. FIG. 19 shows an example system. FIGS. 20-24 illustrate example augmented reality and/or virtual reality devices that can incorporate the concepts described herein, which may in some examples include haptic elements.

FIGS. 1A-1C depict an NVP element with spherical voids, showing significant variations in wall thickness. FIG. 1A shows an approximately cubic portion of an NVP 100 with generally spherical voids 104 embedded in a polymer-based matrix 102. This may be a portion of an NVP element that is a component of, for example, an actuator or sensor. The figure shows a uniform arrangement of spherical voids. The pattern may be repeated in all directions, and only a portion of spherical void 104 is shown in this representation.

FIG. 1B shows a cross-section including the polymer matrix 102 having an arrangement of voids 104 disposed therein. The thickness of portions of the polymer matrix 102 separating the voids 104 may be termed the wall thickness (W). FIG. 1B shows that with this arrangement of voids, there may be significant variation in the wall thickness, with some neighboring voids separated by a first wall thickness W1 that is appreciably greater than a second wall thickness W2 (measured along a different direction) separating other neighboring walls. FIG. 1B shows that the use of uniform spherical voids can lead to a high variation in the thickness of walls between neighboring voids. For example, walls may have relatively thin and thick portions, as shown, and this may lead to uneven compression properties as discussed further below.

FIG. 1C shows how an anisotropic NVP 150 may be formed from an NVP initially having spherical voids. Compression of the NVP along the vertical direction (as illustrated) forms an NVP 150 having oblate spheroidal voids 154 within a polymer matrix 152. As will be discussed further below, anisotropic voids may improve the compression properties of the NVP.

FIG. 2A-2D depict a portion of an NVP having spherical voids, undergoing compression. FIG. 2A shows an NVP 200 having spherical voids 204 within a polymer matrix 202 (detail shown in the inset). The arrows represent application of a compressive force, downwards as shown. FIG. 2B is the same as the inset portion discussed above. The illustrated void 204 is spherical and the illustrated wall portion of the polymer matrix 202 is undeformed. FIG. 2C shows 20% compression. The lower interior surface 206 is partially flattened and raised by the compression, which deforms the void. FIG. 2D shows 30% compression, further raising the lower interior surface into a slightly convex form 208, and inducing buckling in the wall between neighboring voids at 210. The buckling may reduce the mechanical properties of a sensor or actuator application of the NVP. For example, wall buckling may lead to effectively discontinuous changes in sensor or actuator response (to applied deformations or applied electric fields), and may lead to non-reversible stress-strain properties of the NVP. The polymer walls may begin to fold in on themselves in a way that makes the degree of compression difficult to control, for example, through an external electric field. The deformation at 30% and higher compressions may include substantial buckling and may generally be unstable and susceptible to collapsing further than intended or predicted. For example, buckling may reduce the reproducibility of an actuator, and/or the accuracy of a sensor, that uses such an arrangement of voids.

FIG. 3A-3F depict an NVP with improved wall thickness uniformity. FIG. 3A shows how the NVP, shown generally at 300, includes a polymer matrix 302 enclosing an arrangement of voids, such as void 304 (shown partially in this representation, which may be repeated in one or more orthogonal directions). The improved nanovoided polymer (NVP) 300 includes voids with a form-fitting void shape that improves the uniformity of the wall thicknesses. In this example, the void shape is non-spherical, and is configured such that the wall thickness is more uniform across all surfaces.

FIG. 3B further illustrates an example void shape which may be used in the void arrangement of an NVP, such as that shown in FIG. 3A. The repeating unit is shown generally at 310, and includes a portion of the polymer matrix 314 enclosing the non-spherical void 312.

FIG. 3C shows another example representation 320 of a form-fitting void shape with a more uniform wall thickness. The three-dimensional space may be divided into repeating cells, such as cells 330 and 340, which may be identical, that fill the space. The cell may fill a three-dimensional space when a cell is repeated in all directions. An arrangement of three cells is shown, at 320, in the figure, but the pattern may continue in all directions. In some examples, the same cell shape may fill the entire three-dimensional volume (e.g., of an NVP element) when the cell is repeated in all directions, but, in general, the cells do not need to have identical shapes. A form-fitting cell shape may be created using any appropriate method, such as the method described herein.

FIG. 3D shows an arrangement 320 including a rounded approximation to a form-fitting void within the cell. A central volume within the cell 334 subtracted to form a void 332. FIG. 3D renders the cell 334 transparent to show the volume occupied by the void 332. If the cell is repeated in all directions, the resulting shape may be equivalent to that shown in FIG. 3A.

FIG. 3E further illustrates an arrangement 340 of a few such cells, including cell 344 having void 342.

FIG. 3F shows a cross-section 350 of example void shapes, and shows that an arrangement including an example void shape may be referred to as isotropic, if the shape dimensions are the same as measured along orthogonal directions. The figure shows a polymer matrix 352 including a void 354 having orthogonal void dimensions A1 and A2. There may be a third orthogonal dimension A3, which may be normal to the plane of the illustration and is not shown in the figure. The orthogonal directions may be, for example, parallel to and perpendicular to an applied electric field, or parallel to or perpendicular to the plane of the electrodes (e.g., for parallel spaced-apart electrodes). For example, A2 may be parallel to an applied electric field, and A1 and A3 may be perpendicular to an applied electric field. In some examples, the electric field may be assumed to be substantially uniform between parallel electrodes. In some examples, the void dimensions may be the same along three orthogonal directions, which may be those parallel to the edges of the illustrated cubic portion of FIG. 3A. This type of structure (e.g., a repeated cell, or the structure formed therefrom) may be referred to as isotropic, even if the voids are non-spherical. A cell having an isotropic shape may repeat uniformly in all directions. Also, a spherical void shape may be used to provide an isotropic structure as a spherical void has the same internal diameter in all directions.

FIGS. 4A-4B depict a buckling deformation in an isotropic NVP. FIG. 4A illustrates the compression of an NVP, shown generally at 400, having an isotropic void shape and generally uniform wall thicknesses. However, problems with the buckling instability were observed, as represented by the wavy appearance of the walls 412 surrounding the deformed voids 414 in the compressed form 410, shown on the right of FIG. 4A.

FIG. 4B further illustrates an example buckling instability in a closer view, shown as a cross-section 420. The cross-section 420 shows deformed walls in 422 having a wavy appearance surrounding the deformed voids 424.

However, the observed buckling instability that occurred with isotropic voids may be greatly reduced, and in some examples may be substantially eliminated, using an anisotropic void shape. In some examples, an anisotropic void shape may have an internal dimension (e.g., along a direction parallel to that along which an electric field may be applied) that is appreciably less than along an orthogonal dimension (e.g., along orthogonal directions that are perpendicular to a direction along which an electric field may be applied).

FIGS. 5A-5C depict an example anisotropic NVP having improved compression performance, for example, relative to an isotropic NVP. FIG. 5A shows an example anisotropic NVP 500 including a polymer matrix 502 enclosing anisotropic voids 504. The illustrated portion may repeat many times along one or more of the three orthogonal directions (e.g., parallel to the edges of the illustrated cubic portion). In this example, the voids are anisotropic.

FIG. 5B shows a cross-section 510 including polymer walls 512 enclosing an anisotropic void 514. The void 514 may be termed a 2× anisotropic void, as the ratio between a horizontal dimension A1 divided by a vertical dimension A2, in this example, is 2. This ratio may be termed the anisotropy ratio, and in this example the anisotropy ratio A1/A2 is 2. In some examples, A1 may represent the long axis of the void shape, and A2 may represent the short axis of the void shape. In some examples, the void interior dimension may be determined in at least one direction perpendicular to the direction of an applied electric field (or for sensor applications, the direction of compression) may be twice that measured along a direction parallel to the direction of an applied field and/or a compression.

In some examples, A2 may be parallel to the direction of an applied electric field, and/or parallel to a direction of compression, and A1 (and A3) may be perpendicular to an applied electric field, or a direction of compression. In some examples, A1 and A3 may be approximately equal, and the void may be an oblate spheroid. In some examples, a void having an oblate spheroid shape may be considered a flattened or pancake void, and the void shape may be similar to a spherical shape flattened along, for example, the direction of an applied electric field or a direction of an applied compression. In some examples, the electric field may be assumed to be substantially uniform between parallel electrodes. In this example, A2 may be termed the short axis of the void shape, and A1 may be termed the long axis of the void shape.

FIG. 5B also shows that the void shape may be configured so that the wall thickness between void 514 and neighboring voids (such as void 516) is generally uniform, or at least appreciably more uniform than for an NVP including spherical voids.

Finite element simulations of the compression of these nanovoided polymer elements suggest that an anisotropic design may be less susceptible to buckling.

FIG. 5C illustrates simulated compression of the NVP 500, as also shown in FIG. 5A, into compressed form 550. In this example, walls 552 surround deformed voids 554. There is no suggestion of buckling of the walls in the compressed state. Hence, this design of nanovoided polymer element may have greatly improved properties compared with an isotropic design, for example, having improved reproducibility of the actuation-voltage curve.

FIGS. 6A-6B also depict another anisotropic NVP having improved compression properties, in accordance with some embodiments. FIG. 6A shows example anisotropic NVP 600, including a polymer matrix 602 that provides walls between anisotropic voids 604. The design may repeat itself many times in three orthogonal directions.

FIG. 6B illustrates a cross-section 610 in more detail, demonstrating that a representative anisotropic void 614 is a 4× anisotropic void. The anisotropic NVP, shown in cross-section 610, includes voids 610 surrounded by walls 614, the walls being provided by the polymer matrix of the NVP and separating neighboring voids such as void 614 and void 616. In this example, the ratio between a horizontal dimension A1 divided by the vertical dimension A2 (as illustrated) is 4. The void dimension in at least one direction perpendicular to the direction that an applied electric field may be applied (or for sensor applications, the direction that a compressive force may be applied) is, in this example, 4. The anisotropy ratio may be defined by this ratio, and in this illustrated example the anisotropy ratio A1/A2 is 4. In some examples, A1 may represent the long axis of the void shape, and A2 may represent the short axis of the void shape.

FIG. 6C shows a simulation of the compression of a nanovoided polymer element 600, such as shown in FIG. 6A, having a void anisotropy ratio of 4. The compressed state 650 includes deformed (further flattened) voids 654 within walls provided by the polymer matrix 652. In this example, there is no suggestion of buckling in the compressed state 650. Hence, this design of nanovoided polymer element may have greatly improved properties compared with an isotropic design, for example, having improved reproducibility of the actuation-voltage curve.

FIG. 7A-7C show anisotropic NVPs having different void fractions, in accordance with some embodiments.

FIG. 7A shows an anisotropic NVP 700, with a polymer matrix 702 including an arrangement of anisotropic voids 704. The void fraction in this example is 30%.

FIG. 7B shows an anisotropic NVP 710, with a polymer matrix 712 including an arrangement of anisotropic voids 714. The void fraction in this example is 50%.

FIG. 7V shows an anisotropic NVP 720, with a polymer matrix 722 including an arrangement of anisotropic voids 724. The void fraction in this example is 70%. Even with this high void percentage, the wall thicknesses may be generally uniform.

FIGS. 8A-8B depict voltage-actuation curves of NVPs showing improved compression properties, in accordance with some embodiments.

FIG. 8A shows finite element simulation results for polymer actuators with a 70% void fraction (including those in the above figures, and also a configuration with a void anisotropy ratio of 8). The isotropic curve (for an NVP having isotropic voids) initially rises the fastest, and then has a chaotic (non-monotonic) zig-zag region. The chaotic portion of the isotropic curve indicates that a stable applied voltage-actuation relationship does not occur for bulk compressions in the range of 20-60%. The simulations suggest that, starting at 0% bulk compression and increasing the voltage, the structure would collapse from 20% compressed to 60% compressed when a threshold voltage is reached. This behavior is highly undesirable for many actuator applications. For many applications, a smooth, regular, and/or reproducible increase in the voltage-compression curve is desired. The isotropic curve does not show this behavior, and so compression for actuator applications may be limited to 20% or less.

In FIG. 8A, the 2× isotropic actuator curve (the second fastest rising initially) does not show an unstable response as seen in the isotropic curve. However, the curve flattens at about 120 V, and the actuator cannot be precisely controlled beyond this point as the actuation-applied voltage curve is approximately flat. The curve for 2× anisotropy does, however, show a great improvement over the isotropic case. The 4× and 8× anisotropic design curves show that the bulk compression increases monotonically with applied voltage, as desired for improved actuator performance. These anisotropy ratios may lead to excellent actuator performances, that may be reliably controlled.

FIG. 8B shows similar simulations to those of FIG. 8A, for polymer actuators having a lower void fraction (50% void fraction). Similar results were obtained. The isotropic material buckles shortly after 20% compression and it becomes difficult to find a stable voltage that gives a desired compression. Likewise, with the 2× anisotropic material, it is difficult to set a voltage that will give a precise bulk compression over about 30% compression because the curve is nearly flat. However, the 4× anisotropic design provides an actuator that can be reliably operated to 50% deformation and beyond.

FIGS. 9A-9C and 10A-10B depict the relatively insignificant effect of polydisperse voids on the compression properties of NVPs, in accordance with some embodiments.

Simulations indicated that void polydispersity does not greatly change the operational characteristics of a device using an anisotropic NVP.

FIG. 9A shows an anisotropic NVP 900 including a polymer matrix 902 and an arrangement of voids 904. In a device application, the illustrated configuration may repeat in any direction as desired.

FIG. 9B shows, in more detail, the non-uniformity of void sizes within section 910, showing wall cross-sections 912 enclosing different shaped voids 914.

FIG. 9C shows the voltage-deformation plots for both uniform and varying void shapes. An example in which the voids have different shapes performs indistinguishably from an example that has a uniform void shape, and the same void fraction. Hence, only one curve is visible at the illustrated scale.

FIG. 10A illustrates a unit cell of another polydisperse anisotropic NVP. Starting with a non-polydisperse configuration with a uniform void shape (not shown), the unit cell 1000 was modified to add distortion of the polymer walls, so that adjacent voids have different shapes. The figure shows the unit cell, polymer wall cross-sections 1002, and voids such as 1004. Repeating the unit cell in all directions generates a polydisperse element, having non-uniform void shapes. For example, the unit cell 1000 may be reflected in all directions to generate an NVP configuration with non-uniform voids. However, the void fraction and the average anisotropy may remain the same as the initial uniform void shape configuration, allowing a comparison of properties to determine the effect of non-uniform void shapes.

FIG. 10B shows that the performance, as may be represented by a voltage-deformation plot, was not appreciably changed by the generated variations in local void shape. The curves for anisotropic voids with uniform and non-uniform (polydisperse) shapes are overlaid, so that only one curve is observed.

However, NVP properties may be modified using measurable quantities that may be averaged over the entire polymer element, such as the average void anisotropy and the void fraction.

In conclusion, NVPs with anisotropic void configurations may provide significant improvements, compared with NVPs with spherical voids, as they may provide a highly reproducible and precise degree of actuation in response to a given applied voltage.

In some examples, a method of fabricating an anisotropic voided polymer (such as an anisotropic NVP) includes depositing a nanovoided polymer, or a material layer including a polymer precursor, using a deposition process. Examples described herein may refer to nanovoided polymers, but examples may also include voided polymers. A deposition process may include one or more of the following: spin coating, printing, chemical vapor deposition, vapor coating, transfer of a prefabricated polymer layer, dipping, or spraying. The method may further include deforming the nanovoided polymer element (or a material layer that provides an NVP precursor) to form the anisotropic nanovoided polymer element by at least one of the following methods: stretching or tensioning (e.g., using an extrusion process); stretching or tensioning a substrate on which the nanovoided polymer material is deposited; pressing the material; deforming a fluid-based phase (such as emulsions or lyotropic phases) by varying chemical composition, temperature, salt or other component concentration, flow rate, shear rate, agitation, external fields (such as ultrasound, electrical, electromagnetic fields such as optical or UV, or magnetic fields); using shaped nanoparticles that may later be removed (e.g., shaped sacrificial particles); using spherical particles that may be reshaped using temperature or pressure or mechanical stretching/tensioning or a combination thereof, where the particles may include solid polymer nanospheres that may later be removed, and/or where the particles include gas-filled polymer nanospheres that may either later be removed or left within the material. In some examples, the material after deposition and prior to void deformation is partially polymerized (e.g., precured) to a certain degree via polymerization, cross-linking, curing, or some other process using a source of actinic radiation.

In some examples, the anisotropy of the voids may be formed by a process including heating the material prior to and/or during stretching or tensioning. In some examples, the formation of anisotropic voids includes irradiation of the material using one or more radiation sources, such as curing sources, such as UV and/or visible radiation sources.

In some examples, after the anisotropy of the voids is formed, the anisotropy may be “locked in” by one or more further processes, such as a process including further (e.g., complete) polymerization, cross-linking, curing, or some other process. In some examples, “locking in” of void anisotropy may include rendering the void anisotropy substantially permanent, for example, after removing an external factor (e.g., an external field or mechanical input) that induces the void anisotropy. Examples may include irradiating the material layer using UV or visible light, for example, using a source of actinic radiation.

In some examples, an NVP element includes shaped voids, for example, voids having a shape that is changed from the original form of the void when the void was formed. In some examples, after the deformation of the original shape, the aspect ratio of the shaped void may be about 1.5× (alternatively about 2×, alternatively about 3×, alternatively about 5× the original aspect ratio of the emulsion).

In some examples, an anisotropic nanovoided polymer includes a bulk polymer including an arrangement of nanoscale gas-filled voids. The shapes of the voids may be anisotropic, or may be a combination of spherical and anisotropic shapes. In some examples, void shape may vary throughout the material.

In some examples, the deposited material may include one or more of the following: a monomer, polymer, solvent, porogen, surfactant, or emulsifier. In some examples, the deposited material may include nanoparticles, such as polymer nanoparticles, such as polymer nanospheres. Nanoparticles may be solid, hollow, or may include different shell and core materials.

Examples include methods of fabricating anisotropic voids in a polymer. In some examples, voids may be extended arbitrarily along a direction, so that the voids are elongated shaped tubes, which may have, for example, an anisotropic or circular cross-section.

In some examples, anisotropic voids can be generated through mechanical deformation of the polymer in one or two directions (e.g., two orthogonal directions). Mechanical deformation may include one or more processes, such as stretching, pressing, or the like. In some examples, the stretching may include a deformation along at least one direction of at least approximately 1.5×, such as at least approximately 2×, for example, at least approximately 3×, for example, at least approximately 5×. In this context, the “×” may refer to, for example, the ratio of a stretched dimension to the original dimensions of the material. A deformation of 2× may correspond to doubling a dimension along an example direction. There may be an approximately corresponding decrease in at least one direction orthogonal to the stretching direction.

Embodiments of the instant disclosure may include actuators, optical elements (which may include actuators), sensors, and combinations thereof. In some examples, a nanovoided polymer element includes shaped voids in a polymeric matrix. Example applications include nanovoided polymer devices, such as actuators, sensors, and optical elements.

In some examples, a device, such as a polymer actuator, includes nanovoids having generally non-spherical shapes. The nanovoid shapes may be configured to suppress buckling in the material and allow the material to be greatly compressed from its original shape in a controllable manner. The nanovoids may be filled with a fluid (such as a gas, such as air, nitrogen, a dielectric gas, other gas, or other fluid). A functional material may include a nanovoided polymer where the voids are anisotropic in shape. Example anisotropic shapes include prolate shapes (e.g., elongated spheroids), elongate shapes such as cylinders (e.g., with rounded ends), oblate shapes (e.g., flattened spheroids), flattened shapes such as disks, and other geometric shapes. In some examples, a short axis of the void shape is aligned with the direction of compression of the NVP layer. The voids may be distributed periodically throughout the polymer layer, or in some examples may have no long-range periodicity. In some examples, a functional material is constrained to prevent expansion or contraction in one or more directions. In some examples, a nanovoided polymer is used as the dielectric layer in an electrostatic actuator, for example, an actuator that operates via mechanical actuation. The nanovoided polymer material may include one or more polymer components, such as a silicone-based polymer, or an acrylic polymer. The nanovoided polymer element may include an elastomer, and/or a thermoset polymer. The nanovoided polymer material may be actuated through compression or tension in one or more dimensions. For example, the nanovoided polymer material may be actuated through compression or tension in two dimensions.

In some examples, interior surfaces of the polymer matrix (e.g., enclosing the voids) may have a surface layer, such as a coating configured to reduce interactions (e.g., sticking) if interior surfaces come into contact, for example, after compression. A surface layer may include a surfactant, a fluorinated compound such as a fluoropolymer, or other coating.

In some examples, an NVP may be pre-tensioned and/or pre-stretched, for example, before inclusion in a device, such as an actuator and/or a sensor. In some examples, the NVP may be deposited on a substrate, and the substrate may be pre-stretched.

Examples may include polymer devices, such as a polymer actuator. An example actuator includes a long thin block of material, which may include a polymer. A polymer actuator may compress in response to an applied electrical field. The degree of compression may be controlled by controlling the magnitude (e.g., the root mean square (rms) value) of the applied electric field. The actuator may take on a desired configuration and may exert a force on an adjacent surface. In some examples, the actuator may be used to modify an optical element (e.g., adjust the focal length of a flexible lens), or provide haptic feedback.

In example applications, several polymer actuators can be positioned along the rim of a pair of glasses including a flexible lens, such as a lens filled with a liquid. An electric field can be used to move the actuators so that they exert a force on the lens and change the focal point of the lens. Actuators may be configured to move an adjacent surface, for example, by distances up to 1 cm. The electrode separation may be of millimeter or sub-millimeter order to maintain reasonable voltage requirements for the actuator (e.g., less than 1 kV).

An actuator in compression may expand laterally, unless the actuator is laterally constrained, for example, by sidewalls. If the electroactive element of the actuator is constrained so that it cannot expand laterally, the force required to compress a solid electroactive element will be high, particularly if the electroactive element polymer material is close to incompressible. A nanovoided polymer (NVP) material includes many small pockets of air (nanovoids). An NVP is useful as an electroactive element, as it takes less force to compress the NVP than a similarly sized solid polymer element. In some examples, compression of air in the voids requires one or more orders of magnitude less force than that required to compress a solid block of material. Further, the components of air (e.g., nitrogen, oxygen) may dissolve in the polymer under compression, further facilitating compression of the NVP.

Nanovoids may also help enable more precise control over how much the electroactive element deforms in response to a given electric field. In many applications, an ideal actuator will compress gradually as more voltage is applied, and a poor actuator shows instability above a given voltage where the structure rapidly collapses to a very compressed state. An unstable actuator may no longer have a predictable voltage-actuation curve. The voltage-actuation curve may no longer be a monotonic function, and in some examples may show appreciable hysteresis. These effects may be reduced or substantially eliminated using a nanovoided polymer element.

In some examples, a device (such as an actuator and/or a sensor) may include an NVP having voids with a non-spherical shape. Voids may be arranged in a regular lattice, in a random arrangement, or in some other arrangement. The arrangement of voids in the polymer may include one or more of the following. An NVP may include a lattice-like arrangement of voids, such as close-packed, cubic, face-centered cubic, or other arrangement; an arrangement of spheres and/or other non-spherical shapes; anisotropic voids having uniaxial or biaxial orientation; a polymer having the form of a fiber or fiber bundle; an extruded fiber such as an “islands-in-the-sea” microfiber; an extruded form, such as a layer; and/or a 3D printed form.

Improved polymer-based transducers may include non-spherically shaped voids. Examples may include voids having form-fitting shapes which result in increased uniformity of wall thickness compared to spherical voids. Also, configurations include anisotropic may improve the performance of the transducer. An improved NVP-based device may include one or both of anisotropic voids or more uniform wall thicknesses.

In some examples, an NVP element, or a device including an NVP element, may include an NVP having non-spherical voids, such as a form-fitting void shape that results in more uniform wall thicknesses. In some examples, an NVP element, or a device including an NVP element, may include an NVP having anisotropic voids, such as anisotropic voids that provide a monotonic and/or reversible voltage-actuation response. uniform wall thicknesses.

In some examples, an actuator may have one or more of the following properties. An actuator may have a predictable and repeatable actuation response to a specified level of electric voltage. For example, the voltage-actuation response may be generally independent of the actuation history (e.g., whether actuation is increasing or decreasing). In some examples, the voltage-actuation response may be generally monotonic, and may be generally reversible. The actuation mechanism may survive many cycles of extending and retracting. The actuator response time can be sufficiently fast. This depends on applications, but example actuators may have a response time of less than 1 second, for example, from zero to maximum actuation, and in some examples, the response time may be less than 100 msec. In some examples, actuators may achieve a maximum bulk compression of 50% or more.

In some embodiments, nanovoided polymers may be created with spherical nanovoids. In some manufacturing processes, spheres may be the relatively simplest shape to create. Arranging spherical voids for a high void fraction, configurations such as face-centered cubic (fcc) or body-centered cubic (bcc) may be used. However, using a spherical shape may lead, in some examples, to problems. For example, it may not be mathematically possible to fabricate an NVP having spherical nanovoids with a void fraction of over approximately 74%, as this is the packing limit for spherical voids (either in periodic or non-periodic arrangements). In some examples, NVPs having spherical voids and having a void fraction close to a theoretical maximum have very thin walls in some locations and relatively thick walls elsewhere. Also, since the thickness of solid material between voids (wall thickness) can be highly variable with spherical voids, this may encourage a buckling response as the material is compressed. Buckling of the material may lead to a rapid collapse that makes it difficult to control the actuation response with a high degree of precision.

In some examples, an NVP may include an arrangement of voids and have a void fraction greater than 74%, while, in some examples, maintaining generally uniform wall thicknesses.

Example actuators may provide a mechanical component which moves in response to an input electrical signal. Anisotropic voids have spatial non-uniformity that differs in one direction from another direction. Anisotropy may be determined for orthogonal directions, for example, parallel to the plane of the electrodes and normal to the plane of the electrodes. Anisotropy may be determined for directions perpendicular to an electrical field and parallel to an electric field. For example, the mean thickness of an air void may be shorter in the height direction (perpendicular to an electrode) than in the length or width direction (parallel to the electrodes, for the case of parallel electrodes).

Actuation may be measured as a bulk compression. Compression may be measured in absolute units (e.g., a length unit) or as a fraction, for example, the fraction of the deformation relative to an original undeformed dimension of the actuator. For example, if the actuator is compressed and the thickness after compression is 70% of the original uncompressed thickness, then the bulk compression is 30%. In some applications, a monotonic voltage-actuation relationship is desirable. However, the voltage-actuation curve may show unstable and non-monotonic behavior due to buckling, for example, of polymer walls separating neighboring voids. Buckling is a usually undesirable behavior where part of a structure, such as a wall, bends and folds over itself when a load is applied. Buckling is an often undesirable instability that may trigger large deformations, and may greatly reduce in the load driving capacity of the device, such as an actuator.

Nanovoids may include a hole or pore (void) in the solid polymer, and may be filled with a gas (e.g., air, a component of air such as nitrogen, or an inert gas). A nanovoid may have a diameter or other analogous dimension less than 1 micron, for example, in the range 1 nanometer (nm)-1 micron, such as 10 nm-1000 nm. The void fraction is the fraction of volume of the actuator (when in its original state with 0% bulk compression) occupied by voids, for example, by air or an inert gas.

Example applications of the concepts described herein include an electroactive device, such as an actuator, with nanovoids having a non-spherical shape. In some examples, the voids have a form-fitting shape that may result in more uniform wall thicknesses, and may result in a higher void fraction. Increasing the void fraction may be desirable, as compression of gases in the voids may require significantly less energy than that required to compress the material of the polymer matrix. Hence, increasing the void fraction may allow greater actuations (for a given voltage) and/or measurement of greater deformations.

An improved nanovoided polymer element was designed having a form-fitting void shape, resulting in a more uniform wall thickness. A non-spherical void shape was designed such that the wall thickness may be more uniform across all surfaces.

There are a number of possible approaches to determine a void shape that results in a more uniform wall thickness. In some examples, the polymer may be divided into partitions based on distance to the nearest void, for example, using a Voronoi tessellation. A form-fitting shape may then be designed for each partition using one or more of any of the following methods: subtracting a rescaled smaller version of the partition shape; rounding off the corners of the partition shape with a fillet, possibly after rescaling; or creating an approximation to the partition shape using a technique such as Catmull-Clark subdivision, loop subdivision, or a B-spline.

More uniform wall thicknesses may also be obtained using random packing or a periodic lattice arrangement of a 3D space with non-spherical shapes through one or more of any the following approaches: using the same void shape repeatedly, with a random or periodic arrangement; adding random distortions to a base void shape, with a random or periodic arrangement; either of the above, with the void shape scaled to a distribution of different sizes; or any of the above, for example, using a mixture of two or more different void shapes.

An example nanovoided polymer element has voids having an anisotropic shape. Including anisotropic voids may improve the nanovoided polymer element, for example, by reducing the buckling instability, for example, during a deformation of the NVP. A flattened void shape, such as an oblate spheroid shaped void, such as a “pancake” shaped void, may be obtained by stretching the void shape in one dimension relative to the others.

In some examples, the void shapes may be form fitted to an approximate unit cell shape to obtain more uniform wall thicknesses. Voids may be anisotropic (e.g., having different dimensions in plane vs out of plane, where the plane may be perpendicular to the direction of an applied electric field and/or compression). Diameters, or analogous dimensions, along different directions may be configured to bias the voids towards the desired deformation, for example, make the compression less unstable, and to avoid buckling. This may result in a more precise and smooth compression with respect to an applied voltage and/or force. The use of anisotropic voids allows NVP compression that may have improved consistency (e.g., repeatability) for a given applied voltage and/or force. The anisotropy ratio (e.g., a dimension ratio along orthogonal directions) may be greater than 1.5, for example, in the range 1.5-10. Example fabrication approaches may include extrusion (e.g., of a precursor material, such as an NVP with a lower anisotropy ratio) and/or compression (e.g., of a precursor material, e.g., compression along a direction along which an electric field may later be applied in a fabricated device). In some examples, anisotropy may be induced in a non-polymerized material (e.g., an emulsion of fluid droplets within a medium including a polymerizable material such as a monomer), or a partially polymerized material (e.g., including fluid droplets within a medium including a partially polymerized material such as an incompletely polymerized monomer). After (or during) generation of the anisotropy, the anisotropy may be made permanent (or “locked in”) by further polymerization of the polymerizable or partially polymerized material. Further polymerization may include taking a polymerization reaction to effective completion, and/or cross-linking. For example, anisotropy may be locked in during or soon after extrusion, compression, or other anisotropy-inducing deformation of a material. In some examples, an NVP may be pre-stretched before inclusion in a device. Relaxation of the pre-stretch may be resisted mechanically, for example, by mechanically preventing expansion of the NVP along one or more directions. In some examples, a device may include a multi-layer structure, for example, including one or more NVP layers, electrode layers, or other layers. Examples described herein may also reduce hysteresis in the properties of fabricated devices. Advantages of anisotropic voids include a smoother actuation curve (for actuator applications) or sensor response curve (for sensor applications), and may not require repeated identical shapes. Other advantages of anisotropic voids may include more rapid gas absorption from the voids into the polymer matrix. For example, the polymer matrix surface area enclosing a particular void volume may be minimized by using a spherical void shape, so that non-spherical void shapes, and in particular anisotropic void shapes, allow faster gas absorption from the void into the polymer matrix, increasing, for example, the speed of a device response (e.g., actuation speed, or sensor response time). In some examples, the polymer matrix may have additional porosity beyond that provided by the voids, for example, including channels between voids, for example, to allow gas to migrate through the NVP as the NVP is compressed. In some examples, an NVP may include multimodal voids, which may have differing shapes, anisotropy, and the like. An NVP may include some random and/or added non-uniformity without significantly affecting the general device performance. In some examples, device performance may be improved by introducing some degree of anisotropy, for example, an average degree of anisotropy, for example an average anisotropy ratio between 1.5 and 10 (or other range, such as other anisotropy ranges described herein.)

In some examples, heating the polymer film before and/or during mechanical stretching may increase the maximum achievable amount of stretching. In some examples, an elevated temperature may be used to heat a polymer component of the material above the glass transition temperature of the polymer component. In some examples, a multilayer substrate may be used, for example, having a layer that adheres both to a support surface, and to the material.

An example apparatus configured to fabricate an anisotropic NVP may include an apparatus configured to stretch a material. Stretching may be accompanied by heating the material and/or the substrate, for example, using a heating element. Other approaches to heating may be used. In some examples, a heating element may be used to heat one or more of the substrates and/or the material. For example, a heating element may include one or more IR sources, which may, for example, be located above and below the substrates. In some examples, the substrates may absorb IR energy and heat up. Heating of the substrates may be used to heat the material. In some examples, the substrates may transmit IR energy to the material, which may then heat up. In some examples, a material may be stretched in two directions, for example, sequentially or simultaneously.

The material may include an NVP, such as an NVP with isotropic voids, or a precursor material, such as an emulsion or partially polymerized material, that may be fully polymerized after formation of anisotropic voids (or precursor droplets) in the material.

A device configured to fabricate an NVP having anisotropic voids may include actuator may be configured to stretch a material, such as an NVP layer, and the actuator may include a stepper motor, other motor, or other type of actuator mechanism. In some examples, a stretcher apparatus may include a load cell or other sensor that may be configured to monitor the degree of stretching and/or the stretching force applied to the material. The substrate may be a flexible substrate, and a material may be deposited on the substrate and subsequently stretched. In some example, the substrate may include an intermediate layer, for example, to enhance adhesion of the material to a substrate. In some examples, a substrate may include a portion of a conveyor belt or similar support surface. The substrate may include an intermediate layer, for example, between the material and a support surface such as a conveyor belt. Grippers may clamp on an edge of the substrate, or may be otherwise connected to the substrate. In some examples, a linear arm may be connected along an edge of a substrate, or a material, directly, using a connector that connects along the length of the edge, rather than using discrete grippers.

In some examples, a material may be compressed along a predetermined direction, for example, by applying a pressure to one or more surfaces. In some examples, a pressure may be exerted by a compression stage, which may include one or more of any of the following: an actuator, a roller, a compression stage (such as a mechanical press), or other force exertion mechanism. The material may expand laterally (e.g., along directions in a plane normal to the direction of pressure), and voids may be elongated along the expansion directions. In some examples, expansion may be prevented along some directions, for example, by walls or other constraining structures, allowing the anisotropic form to be controlled.

In some examples, one or more external fields may be used to obtain anisotropic voids in a material, such as an electric field or a magnetic field. In some examples, a magnetic field may be used to distort the fluid droplets and provide anisotropic voids. In some examples, a material (e.g., an emulsion) may be deformed by flow-related and/or viscous effects, such as one or more of the following: flow, a shear gradient, passage through an orifice, or other approach. In some examples, vibrational inputs or acoustic/ultrasound fields may be used to obtain anisotropic voids. A method of obtaining an anisotropic voided polymer may include forming a fluid phase (such as an emulsion) including spherical fluid droplets (e.g., droplets within a medium, such as a liquid medium), deforming the fluid droplets using an external input (e.g., an electric or magnetic field, or other approach, such as a flow or vibration based deformation), and then polymerizing the medium. The medium may be polymerized, to a complete or partial degree, while the external input is applied. For example, an electric field may be applied, and the medium may be polymerized, to some degree, while the electric field is applied. For example, an electric field (or other external input) may be applied for at least a first time period, during which the droplets deform, and a second time period, during which some degree of polymerization occurs (e.g., partial or full photopolymerization). Polymerization may continue after removal of the external input.

In some examples, a liquid medium may be polymerized while an electric field and/or a magnetic field is applied. Polymerization may then provide a material having anisotropic fluid-filled voids in a polymer matrix, such as an anisotropic nanovoided polymer. In some examples, fluid may be removed from the anisotropic voids, leaving anisotropic voids with a gaseous filling. In some examples, the material may be formed on any appropriate substrate, and the substrate may be stretched by rollers, a roller and a fixed connection, a moveable arm mechanically coupled to an edge of the substrate, or any other appropriate approach.

In some examples, an electrical or magnetic field may be applied to the material while the material is supported by the substrate, and may be applied as the material is being stretched by deformation of the substrate. In some examples, a substrate (e.g., a conveyor belt) may include electrically conducting elements, such as a pattern of interdigitated electrodes, that may allow application of in-plane or out-of-plane electric fields.

In some examples, the material may be stretched by rotation of rollers at different speeds, or in opposite directions, or some combination thereof. In some examples, a control circuit may be used to one or more of: start; stop; slow down; or speed up one or more rollers, for example, to adjust stretching forces on the material (e.g., to apply, remove, or change such forces).

In some examples, an electrical or magnetic field may be applied to the material as a material is stretched by any approach described herein. For example, a material may be supported by a substrate, and the substrate may be stretched as an electric, magnetic, or other field is applied to the material. A substrate may include a conveyor belt (or similar support layer), an intermediate layer, or any other support layer.

In some examples, an anisotropic NVP may be fabricated using a void collapse approach, in which a fluid component is removed (in whole or in part) from voids, which may induce shrinkage preferentially along a direction. For example, a void collapse approach may include shrinkage along a direction in which the material is not restricted. For example, shrinkage may be along a direction orthogonal to the surface of a substrate on which the material is deposited. Anisotropic voids may be elongated along directions within a plane parallel to the substrate surface, and may have, for example, an oblate spheroid shape.

In some examples, void collapse may be assisted by capillary forces acting on the volatile liquid during extraction of the volatile liquid. Using a volatile liquid with a higher surface tension (e.g., compared with any high boiling liquid) may enhance this effect. The achieved anisotropy can be tuned via the ratio of the low/high boiling point solvents. The material may then be fully polymerized, for example, using UV. Heating may be used, or increased, to drive out the high boiling point solvent. This method allows anisotropic voids to be formed within individual layers of deposited material in a multilayer configuration, without affecting the anisotropy of other layers.

FIGS. 11A-11B show example configurations (e.g., arrangements and shapes) of first and second electrodes on a nanovoided polymer element. In these examples, the NVP element is shown as a rectangular block, which may represent an nanovoided polymer element having anisotropic voids. FIG. 11A shows an arrangement of upper electrodes and a common lower electrode. FIG. 11B shows application of an electric field to opposed electrodes.

FIG. 11A shows a device 1100 including a nanovoided polymer (NVP) element 1102 having a first plurality of electrodes (such as electrodes 1104 and 1112) on a first surface and a second common electrode 1106 on a second surface of the NVP element. The second electrode may act as ground plane electrode for some or all of the first plurality of electrodes. A voltage source 1108 allows application of electrical signals between electrodes. For clarity, only electrical connections to electrodes 1112 and 1106 are shown. In some examples, a control circuit with a plurality of electrical connections may be used to apply electrical signals to some or all of the plurality of electrodes, and/or the common electrode. Applied electrical signals may include alternating voltages and/or direct voltages.

FIG. 11B shows a first plurality of electrodes (such as electrodes 1104 and 1112) disposed on an NVP element, in a similar manner to that shown in FIG. 11A. In this example, the second surface of the NVP element supports a second plurality of electrodes (such as electrodes 1110 and 1114). In this example, the first and second pluralities of electrodes (in this case, first and second electrode arrays) are positionally aligned with respect to each other. For example, electrode 1112 (of the first plurality of electrodes) is located in positional registration with electrode 1114 (of the second plurality of electrodes). An electric field applied between electrode 1112 and electrode 1114 may be generally normal to the surfaces of the NVP element on which the electrodes are deposited. In some examples, anisotropic voids may be elongated along at least one direction parallel to the direction of the applied electric field.

In some examples, an NVP element may have an array of stripe electrodes on one surface, and an orthogonal array of stripe electrodes on the opposite surface. Electrical signals may be applied between opposite portions of the electrodes using a multiplexing approach.

Segmental actuation and/or segmented sensor signals may be determined by the size of the stimulated electrode pair, for example, the area of one or both electrodes, and their separation. Each electrode element may be physically and/or electrically separated from one another to limit electrical cross-talk between neighboring electrode element, such as between pixels of a pixelated electrode array.

FIGS. 12A-12C show cross-sectional views of electrode arrangements and the corresponding actuated states of example electroactive devices. FIG. 12A shows a device 1200 including a nanovoided polymer (NVP) element 1202, a plurality of electrodes on a first surface of the NVP element, including electrode 1204, and a common electrode 1206 disposed on a second surface of the NVP element. In some examples, a control circuit may be used to apply variable voltages to one or more of the plurality of electrodes on the upper surface of the NVP element. The figure shows an undeformed structure. In some examples, an NVP element may be formed having an irregular structure, such as having an undulating surface, which may be effectively planarized or otherwise deformed using appropriate electrical signals applied, for example, to electrodes of the plurality of electrodes as a function of position.

FIG. 12B shows a spatially varying deformation of the NVP element 1202 that may be induced by applying different voltages to each of the plurality of electrodes. The figure shows a voltage source 1210 that may be used to apply the voltage between one or more electrodes of the plurality of electrodes and the common electrode. For illustrative clarity, only an electrical connection to an electrode 1208, of the plurality of electrodes, and common electrode 1206 is shown. In some examples, a control circuit with a plurality of electrical connections may be used to apply voltages between, for example, each of the plurality of electrodes (such as electrodes 1204 and 1208) and the common electrode (1206). In some examples, the voltage applied to each of the electrodes of the first plurality of electrodes may have a repeating variation, such as an approximation to a sinusoidal, square-wave, or triangular wave variation. This may be used to obtain, for example, a corresponding periodically repeating deformation of the NVP element. In other examples, the deformation may not have a periodic variation, and may include a non-periodic undulation, concave deformation, convex deformation, parabolic deformation, or other form of repeating or non-repeating spatial variation. Example approaches may be used to obtain electrically-controllable diffractive, reflective, refractive, holographic, or other forms of optical elements.

The degree of deformation (e.g., electrically-induced constriction) between the electrodes may be controlled by adjusting the voltage between one or more of the plurality of electrodes and the common electrode, for example, as a function of the position of the electrodes. In some examples, the upper surface of the NVP element may have an electrically controllable curved surface, which may be used for example, in an electrically-controlled optical element, such as an electrically-controlled lens or mirror. For example, a smooth concave or convex upper surface may be obtained by applying electric signals having a magnitude (e.g., DC voltage, or RMS voltage) that is an appropriate function of position.

In FIGS. 12A-12B, the common electrode 1206 may be a rigid electrode, or may be deposited on a rigid substrate. In some examples, the deformation occurs mostly on the first surface (the top surface, as illustrated) and may be controlled, for example, by varying the applied voltage to each electrode as a function of position. The surface deformation may include, for example, one or more of: an undulating structure, a parabolic or other curved structure (e.g., either convex or concave), an oblique structure (e.g., a tilted surface formed by an approximately linear degree of deformation as a function of position), or other structure.

Electrical potentials may be applied between each electrode (or between selected electrodes) of a plurality of electrodes and a common electrode may be used to obtain a desired surface deformation, for example, an undulating pattern, a curved deformation (such as a concave or convex mirror), a tilt, and the like. This approach may be used to generate a desired haptic feedback, texture, or optical property (e.g., a diffraction grating, or spatially variable phase delays, for example, to create interference fringes). The root mean square (RMS) magnitude and time dependence of applied fields may be varied to obtained desired dynamic (time-varying) properties. For example, the applied electrical signal may be modulated to obtain a tactile sensation. In FIG. 12B, the lower surface of the NVP does not distort, for example, due to a relatively rigid underlying substrate (not shown). In some examples, such as discussed elsewhere, both surfaces of the NVP (and any attached flexible substrates) may distort. In some examples, the thickness of the NVP layer may vary laterally, for example, having alternating relatively narrow and relatively thicker regions. For example, the thickness variation may be oscillatory, tapered, or otherwise varying. In some examples, a sinuous distortion may be obtained. Reflective, refractive, and/or diffractive optical elements may be obtained using this approach.

FIG. 12C shows another example configuration, in which each of the first and second opposed surfaces of the NVP element support a plurality of electrodes. The figure shows a device 1220 including an NVP element 1222 having a first plurality of electrodes (such as electrode 1224) on one surface, and a second plurality of electrodes (such as electrode 1226) on the second surface.

In some examples, a control circuit with a plurality of electrical connections may be used to apply voltages between, for example, each of a first plurality of electrodes on a first surface and a corresponding (e.g., opposed) electrode of a second plurality of electrodes on a second surface, or between some other combination of electrodes. In some examples, the thickness of the NVP element may vary with position based on the magnitude of electric signals applied between different pairs of electrodes. In some examples, the NVP may take on an undulating configuration, for example, based in part on voltages applied between laterally offset electrodes on opposed surfaces. In some examples, the deformation of the NVP element may include a spatially varying thickness and a spatially varying undulation.

The degree of deformation (e.g., electrically-induced constriction) between the electrodes may be controlled by adjusting the voltage between one or more of the corresponding pairs of opposite electrodes, for example, as a function of the position of the electrodes. In some examples, the upper surface and/or the lower surface of the NVP element may have an electrically controllable curved surface, which may be used for example, in an electrically-controlled optical element, such as an electrically-controlled lens or mirror.

In some examples, the actuator may be in contact with another flexible and conformal substrate. The actuation can generate a force or displacement of that substrate. It can also generate changes in capacitance, resistance, and optical properties such as refractive index or optical phase of the nanovoided polymer. The nanovoided polymer under individual electrode can be switched using an active matrix backplane or a passive matrix backplane. Flexible backplanes made from organic thin film transistors and stretchable interconnects may also be used. For sensing, the perturbations can be in the form of mechanical or thermal inputs that can be sensed by this sensor.

In some examples, a nanovoided polymer (NVP) element may be used as a transmissive optical element where the actuated state of the device may be a lens or a grating. In some examples, both the first and second electrodes are transparent. In some examples, an optical element may be driven by a transparent active matrix such as transparent nanowire transistor circuitry. In some examples, a device may include a reflective optical element. In such cases, the NVP (or the electrodes) need not be transparent, for example, if the reflective element (e.g., a mirror) is on the outer surface so that light does not pass through the NVP element. In some examples, one electrode may be transparent and/or may be stretchable, and the other electrode may be reflective.

In some examples, an electric field may be applied between laterally offset electrodes, which may provide a lateral component to the electrical field and hence electroactive constriction along a direction, for example, parallel to the surfaces of the NVP on which electrodes are supported. In some examples, bending may be obtained. In some examples, lateral fields may be applied between electrodes on the same surface. Electrodes may be arranged in any desired arrangement, such as a 1D or 2D array, a sinuous pattern, irregular pattern, and the like. In some cases, an electrode may be elongated, for example, disposed on the surface as a stripe electrode. Electrode stripes may be straight (e.g., a highly elongated rectangular shape), wiggly, or wavy.

FIG. 1300 depicts an exemplary electrode arrangement in accordance with some embodiments. As shown in this figure, a device may include an NVP element 1300 having a plurality of electrodes (such as electrode 1302) on a first surface, and a second plurality of electrodes (such as electrode 1304 and 1306) on a second surface. A control circuit (not shown) may be used to apply voltages V₁ . . . V₈ to each (or some) of the various illustrated electrodes. For example, there may be electrical potential differences (voltages) between various electrodes, for example, between V₁ and V₅, V₂ and V₆, V₃ and V₇, and/or between electrodes V₄ and V₈. Selective compression of an end portion may be achieved by applying an electrical potential across an end portion, for example, between electrode 1302 (at potential V₁) and electrode 1304 (at potential V₅), or between potentials V₄ and V₈. For compression of a central region, an electrical potential may be applied between opposed electrodes within the central portion, for example, by applying differing electrical potentials at V₂ and V₆, and/or between V₃ and V₇. It is also possible to obtain a component of in-plane electrical field (and hence in-plane compression) by applying an electrical potential between laterally offset electrodes, for example, using a potential difference between V₁ and either V₆, V₇, or V₈. Other electrodes may float (e.g., be electrically isolated), be grounded, or have some other electrical potential applied to them.

Furthermore, a control circuit may be used to dynamically adjust electric potentials to provide vibratory or other oscillatory deformations, which may be used to provide haptic feedback.

FIG. 14 shows a further example of a deposition apparatus, which may additionally be used to form one or more additional layers on an NVP fabricated using a process including a phase inversion. The apparatus 1400 may include a rotating drum 1430 having a surface 1432, chamber wall 1434, drum heater 1436, one or more material sources (in this example, first material source 1410 and second material source 1428), one or more vaporizers (in this example, first vaporizer 1415 and second vaporizer 1426), one or more radiation sources (in this example, first radiation source 1420 and second radiation source 1422), and an electrode material source 1424. For example, the first vaporizer may be used for polymer deposition related to NVP formation, and second vaporizer may be used for polymer deposition related to the formation of the additional layer. Radiation sources 1420 and 1422 may be used for, for example, for polymerization (e.g., curing) of polymer precursors (e.g., monomers), surface melting, or other suitable purposes. The electrode material source may be configured to deposit, for example, metal or electrically conductive metal oxide films onto an NVP element.

In some examples, the apparatus of FIG. 14 may be used for the fabrication of an electroactive device (e.g., an actuator), including a nanovoided polymer element. In some examples, apparatus 1400 may be used for fabricating an electroactive device having electroactive polymers with nanovoids, and additional layers such as electrodes formed thereon.

Any fluid (e.g., one or more solvents) remaining in the voids may be removed after partial polymerization and before deforming the voids, or may be removed after polymerization is complete. A fluid may be removed from the polymer voids using one or more of the following: a change in temperature (e.g., an increase temperature), pressure (e.g., a reduced pressure), a solvent exchange (e.g., introducing a different fluid into the voids with one or more favorable properties), or other process that removes the fluid from the partially or fully cross-linked polymer to produce a voided polymer.

In some examples, a deposition apparatus may include one or more radiation sources, for example, for polymerization and/or cross-linking of the material. In some examples, a single radiation source may be used (e.g., as a curing source). In some examples, the same radiation source may be used to partially polymerize the polymer film before deforming the material (and the voids in the material), and also to fully polymerize the film after deforming the material. In some examples, initial partial polymerization and complete polymerization may be performed using different radiation sources. Radiation sources may include actinic radiation sources (which in some examples may refer to UV-visible radiation sources, configured to provide UV and/or visible radiation).

Deposited monomers may be monofunctional or multifunctional, or mixtures thereof. Multifunctional monomers may be used as crosslinking agents to add rigidity, or to form elastomers. Multifunctional monomers may include difunctional materials such as bisphenol fluorene (EO) diacrylate, trifunctional materials such as trimethylolpropane triacrylate (TMPTA), and/or higher functional materials. Other types of monomers may be used, including, for example, isocyanates, and these may be mixed with monomers with different curing mechanisms. A deposited polymer precursor may be combined with a sacrificial material (e.g., a liquid that may be subsequently evaporated to provide a nanovoided structure). In some examples, a deposited polymer precursor may be combined with nanoparticles (e.g., metal or dielectric nanoparticles) to, for example, increase the dielectric constant of the formed polymer materials.

In some embodiments, a deposition apparatus may include one or more vaporizers, and each of the one or more vaporizers may apply a different material, for example, one or more of the following: monomers or other polymer precursors, surface energy modifiers (e.g., to modify the surface energy of a substrate, to enhance or eliminate wetting and/or infusion, etc.), a sacrificial material such as a liquid that is subsequently evaporated to leave a void, a ceramic precursor such as an ormosil precursor, such as tetraethyl orthosilicate and water, other polymerizable and/or non-polymerizable materials, surfactants, other emulsion promoters, phase inversion promoters, or a catalyst for forming a sol gel such as HCl or ammonia.

In some examples, a deposition apparatus may be configured to deposit an emulsion promoter onto the surface, or onto the precursor layer. The emulsion promoter may induce (or help induce) emulsification in the precursor layer. An emulsion promoter may include a salt, a pH adjuster, a surfactant, or the like.

In some examples, a deposition apparatus may be configured to deposit a phase inversion promoter onto the precursor layer. The phase inversion promoter may induce (or help induce) phase inversion in the precursor layer. A phase inversion promoter may include a salt, a pH adjuster, a surfactant, or the like.

In some examples, a deposition apparatus may include one or more further heaters, other sources, additional exhaust ports, and the like. Pressure may be adjustable, to extract liquid components from a polymerized element. Ranges may be inclusive, and range limits approximate. In some examples, waste liquid components may be directed in certain directions to avoid contaminating sources of deposited materials, for example, using some combination of heating, a directed gas flow, a lower pressure exhaust chamber, closing ports associated with sources, and the like.

A deposition apparatus may further include one or more additional nozzles (e.g., vaporizers, radiation sources, and the like), for example, an additional nozzle for plasma treatment of the NVP surface before deposition of the planarization layer. A plasma treatment may be used to modify the surface structure of the planarization layer, for example, generating free radicals or other chemical moieties. The surface modification may help exclude components of the planarization layer from entering the voids (e.g., pores) of the NVP as the planarization layer is deposited on to the surface of the NVP. In some examples, a planarization layer material may be used to form the planarization layer that has appreciably higher surface energy than that of the NVP (or surface treated NVP, if appropriate).

In some examples, an example nanovoided polymer (NVP) includes anisotropic voids. Isotropic (spherical) voids may lead to non-uniform wall thicknesses, and may lead to unstable buckling under compression. In some examples, non-spherical voids allow more uniform wall thicknesses, improving mechanical response properties. In some examples, anisotropic voids allow smoother and more reproducible electroactive response curves. Voids may be appreciably wider (e.g., in the plane of the electrodes, or perpendicular to the direction of an electric field, or direction of compression) than tall, and the anisotropy ratio (which may also be termed a dimension ratio or anisotropy ratio) may range from, for example, at least 1.5, such as at least 1.7, for example, at least 2, up to, for example, 10. The anisotropy may favor compression in a direction normal to the plane of the electrodes, and may lead to improved voltage-actuation response curves, for example, by reducing the effects of buckling an allowing a monotonic voltage-actuation response curve. Manufacturing approaches may include extrusion, compression, phase separation, partial void collapse under solvent removal (e.g., to give disk-shaped voids), and the like. Applications may include actuators, sensors, and other transducer devices. Similar approaches, such as anisotropic voids, may be used on larger size scales, such as microscale anisotropic voids. Actuator response times may be longer with larger voids, particularly for closed void configurations, depending on the appropriate gas solubility of the polymer used. In some examples, the relative gas solubility (e.g., the relative air solubility) of the gas in the polymer may be greater than 0.001, such as greater than 0.01, for example greater than 0.1. A higher relative gas solubility may allow improved response times (e.g., an actuator response time, a sensor response time, or other electroactive device response time), and/or reduced hysteresis or creep. For example, silicone polymers (such as PDMS) may have excellent air solubility. Example polymers may be elastomers, may include, for example, silicone or acrylic polymers, and may be thermoset or otherwise cured.

FIG. 15 shows a voided polymer material including a periodic array of voids. FIG. 15 shows a voided polymer material 1500, including a periodic array of anisotropic voids 1520 in a polymer matrix 1510. In this example, as illustrated, the anisotropic voids 1520, shown in cross-section, have an internal horizontal dimension that is appreciably greater than the internal vertical dimension, and hence have appreciable anisotropic shape. In some examples, the voids may have a generally prolate spheroid shape. In some examples, voids may have a generally oblate spheroid shape, or another shape having the illustrated cross-section. In some examples, the voids may include nanovoids having an internal dimension of less than approximately 1 micron.

In some examples, voids, such as nanovoids, may be arranged in a regular array, with periodic variations in one, two, or three orthogonal directions. However, in some examples, there may be no regularity to the arrangement of voids in the polymer matrix.

FIG. 16 shows an example method of operation of a device, for example, a device including a first electrode, a second electrode, and an anisotropic nanovoided polymer located, at least in part, between the first electrode and the second electrode. An example method 1600 may include applying an electric field between the first electrode and the second electrode of the device (1610); inducing a contraction of the anisotropic nanovoided polymer (1620), where the contraction may include a contraction along a direction of the electric field; and (optionally) mechanically coupling the contraction to a haptic output (1630). In some examples, the device may be a haptic device. In some examples, an actuator may be used to control a mechanical, electrical, or optical element, such as a moveable element (such as a position adjuster for a supported component), a variable electrical component (such as a tunable capacitor or other adjustable component), or to control the optical properties of an adjustable optical component (such as a lens, mirror, diffractive component, or holographic element). In some examples, the contraction of the nanovoided polymer along the electric field may include a deformation of anisotropic voids, which may be elongated in at least one direction perpendicular to the electric field. For example, the anisotropic voids may have an oblate spheroid shape (even with no electric field applied), and may be elongated within a plane perpendicular to the electric field (or, elongated within a plane parallel to the plane of at least one electrode, such as the first electrode). The anisotropy of the voids may increase as the electric field is increased.

Application of an electric field to an anisotropic NVP may induce contraction, through electro-constriction of an electroactive polymer matrix. A control circuit may be used to modulate the electro-constriction, for example through the application of voltage pulses between the electrodes. In some examples, an oscillatory mechanical vibration may be electrically induced in the actuator.

In some examples, shaped voids may be formed using shaped particles that may be added to the material. Sacrificial particles may then be later be removed from the material. For example, anisotropic sacrificial particles may be added to a material, and then removed to leave anisotropic voids in the material. In some examples, particles may include hollow particles, such as anisotropic hollow particles. For example, hollow particles may include nanoballoons that may be added to a material, and may remain in an anisotropic nanovoided polymer. In some examples, the interior of a hollow anisotropic particle, such as the interior of a nanoballoon, may provide the anisotropic void. In some examples, particles may be initially spherical, and may then be deformed to form anisotropic particles by any appropriate method, such as the methods described herein for forming anisotropic voids. Example methods may include heating a material to facilitate deformation of particles into anisotropic particles. For example, hollow particles such as nanoballoons may be deformed at an elevated temperature. In some examples, particles may include polymer particles, such as hollow polymer particles. In some examples, particles may be heated above a glass transition temperature of a polymer component of a particle.

Shaped voids may also be formed using deformations of emulsions, lyotropic phases, or other soft matter phases, using applied fields, such as electrical or magnetic fields, and these may be applied in sequence with or concurrently with other deformations such as stretching, or as one or more material components are polymerized.

In some examples, spatial variation in material properties may be introduced, for example, by introducing variations (e.g., temporal and/or spatial variation) in one or more of the following: chemical composition, temperature of the material, salt or other component concentration, flow rate, agitation, vibrational amplitude, or external field strength (e.g., of ultrasound, electrical, or electromagnetic fields, such as optical or UV, or magnetic fields).

In some examples, shaped voids may be generated through nanopatterning using phase masks on photosensitive elastomers. Shaped voids may also be formed using a gas-diffusion expansion process.

Nonuniform void shape distributions may be achieved by applying a gradient in intensity of the radiation source throughout the partial polymerization. In regions subject to greater radiation intensity (and/or greater irradiation time, or other measure of effectiveness such as wavelength), polymerization may advance further. This may lead to a spatial variation in the Young's modulus of the material. When the material is stretched, a region with a lower Young's modulus may stretch more, and voids in those regions may have a larger anisotropy after stretching, compared to voids in regions having a higher Young's modulus.

In some examples, a deposition process (e.g., a printing process, such as ink jet printing) may allow deposition of a material having a spatially variable composition. For example, there may be a spatial variation in one or more of the following: concentration of crosslinker, material composition (e.g., monomer composition), and the like. After full or partial polymerization, there may be a spatial variation in a material property, such as Young's modulus, allowing a spatially varying anisotropy of voids.

In some examples, the Poisson ratio of the polymer emulsion may determine the aspect ratio of the spherical voids after the stretching of the film. The Poisson ratio relates to the amount of vertical compression to a certain amount of transverse stretching.

When the material is used for dielectric applications, pre-stretching may have beneficial effects on the dielectric performance. Pre-stretching the film may increase the pressure inside of the material, pushing volatiles out of the voids, and thereby increasing the breakdown voltage.

FIG. 17 illustrates an example method 1700 of forming a voided polymer element, such as a nanovoided polymer element, or of making an electroactive device including one or more such elements. Example methods may include, for example, forming an emulsion including fluid droplets within a liquid medium (1710). The method may further include partially polymerizing the liquid medium to form fluid droplets in a (partially polymerized) material layer (1720); deforming the material layer to form anisotropic fluid droplets within the material layer (1730); and polymerizing the material layer to form anisotropic voids in a polymer element (1740). In this example, the term “anisotropic voids” may include anisotropic fluid droplets (e.g., in a polymer matrix), and the term “anisotropic voided polymer” may include a polymer including anisotropic voids. In some examples, the term void may not necessarily refer to the absence of material, and may refer to a non-solid portion of a solid matrix. For example, fluid-filled regions of a polymer matrix may be referred to as voids. Example methods may optionally further include removing the one or more liquid components from the polymer element, for example, to replace a fluid with another fluid, such as another gas or liquid. Example methods include methods of forming an anisotropic voided polymer element, for example, including anisotropic voids within a polymer matrix. The voids may include nanovoids. Examples may further include depositing a pair of electrodes on the anisotropic voided polymer element, so that at least a portion of the anisotropic voided polymer element is located between the pair of electrodes. The pair of electrodes may be part of a larger plurality of electrodes. Example methods may further include fabrication of an actuator and/or sensor device using the anisotropic voided polymer element, for example, using the pair of electrodes to apply an electric field to an anisotropic nanovoided polymer element, or to receive electrical signals from the pair of electrodes in response to a deformation of the anisotropic nanovoided polymer element.

FIG. 18 illustrates an example method 1800 of forming a voided polymer element, such as a nanovoided polymer element, or an electroactive device including one or more such elements. Example method 1800 may include, for example, forming voids in a polymer matrix (e.g., as an array or irregular arrangement of voids) at step 1810. The example method may further include deforming the polymer matrix to form anisotropic voids in a polymer matrix (step 1820). This may be termed an anisotropic voided polymer. The example method may also optionally include depositing electrodes on an anisotropic voided polymer (step 1830), so that, for example, at least a portion of the anisotropic voided polymer is located between a pair of electrodes. Electrodes may be formed directly on a surface of the anisotropic voided polymer or may be formed on one or more intermediate layers disposed thereon.

In some examples, a device includes an anisotropic nanovoided polymer including anisotropic nanovoids in a polymer matrix, a first electrode, and a second electrode. At least a portion of the anisotropic nanovoided polymer may be located between the first electrode and the second electrode. The anisotropic nanovoids may include oblate voids, such as oblate nanovoids. In some examples, an oblate nanovoid may be a nanovoid having an internal dimension of less than 1 micron. In some examples, an oblate nanovoid may have a generally oblate spheroidal shape, having an equatorial diameter greater than an (orthogonal) polar diameter. In some examples, an anisotropic nanovoided polymer may include prolate nanovoids, for example, nanovoids having a generally prolate spheroidal shape (e.g., having a polar diameter greater than an equatorial diameter). In some examples, a pair of electrodes may be spaced apart and generally parallel to each other, and the anisotropic nanovoided polymer may be a layer located at least in part between the pair of electrodes. The pair of electrodes may be part of a plurality of electrodes. In some examples, the equatorial plane of oblate spheroids may be generally parallel with the plane of one or more electrodes. For example, the oblate nanovoids may have a dimension parallel to the electrodes that is appreciably greater than a dimension perpendicular to the electrodes. In some examples, prolate nanovoids may have a dimension parallel to the electrodes that is greater than a dimension perpendicular to the electrodes. In some examples, a degree of anisotropy may be defined as the magnitude of a ratio of a dimension parallel to the electrodes to a dimension perpendicular to the electrodes. The degree of anisotropy may be at least approximately 1.5, and in some examples, may be at least approximately 2.

In some examples, a device includes a nanovoided polymer element (including an arrangement of voids), a first electrode, and a second electrode, where the nanovoided polymer element is located at least in part between the first electrode and the second electrode, and the arrangement of voids includes anisotropic voids, the anisotropic voids having a first dimension greater than a second dimension. The first dimension may be measured along a first direction, and the second dimension may be measured along a second direction. For example, the first and second directions may be orthogonal. In some examples, a device may further include a control circuit configured to apply an electrical field between the first and second electrodes. In some examples, the electrical field may be applied generally parallel to the second direction.

In some examples, a device includes anisotropic voids, and the anisotropic voids may have an anisotropy ratio determined by a ratio of a first dimension measured parallel to the first electrode divided by a second dimension measured perpendicular to the first electrode. In some examples, the anisotropy ratio may be between approximately 1.5 and approximately 10. In some examples, the anisotropy ratio may be between approximately 2 and approximately 10. In some examples, the anisotropy ratio may be between approximately 2 and approximately 8. In some examples, the anisotropy ratio may be between approximately 4 and approximately 8. In some examples, the arrangement of voids may be configured so that polymer wall thicknesses between neighboring voids are generally uniform.

In some examples, a device includes a nanovoided polymer element (including an arrangement of voids), a first electrode, and a second electrode, where the nanovoided polymer element is located at least in part between the first electrode and the second electrode, and the arrangement of voids is configured so that polymer wall thicknesses between neighboring voids are generally uniform. In some examples, the arrangement of voids includes anisotropic voids, the anisotropic voids having a first dimension greater than a second dimension. The anisotropic voids may have an anisotropy ratio determined by a ratio of a first dimension measured parallel to the first electrode divided by a second dimension measured perpendicular to the first electrode. In some examples, the anisotropy ratio may be between approximately 1.5 and approximately 10. In some examples, the anisotropy ratio may be between approximately 4 and approximately 8.

In some examples, the device may be, or include, an actuator and/or a sensor. The device may further include a control circuit configured to apply an electrical potential between the first electrode and the second electrode. The device may be a spatially addressable actuator. In some examples, the device may be flexible, and may be conformed to an underlying substrate.

Application of an electrical signal between the first electrode and the second electrode may induce a deformation of the nanovoided polymer element. In some examples, the device may be (or include) an electrically controllable optical element. The device may include one or more of a mirror, a lens, a prism, a grating, a phase plate, a diffuser, a holographic element, a beam splitter, a beam combiner, or an optical filter.

In some examples, a computer-implemented method includes applying an electrical signal between the first electrode and the second electrode of an electroactive device, such as a device as described herein, to obtain a desired surface deformation of the electroactive device.

In some examples, a system includes at least one physical processor, and physical memory including computer-executable instructions that, when executed by the physical processor, cause the physical processor to apply electrical signals to the device, such as a device as described herein, to obtain an actuation of the device. In some examples, a system may include a haptic device, and the desired surface deformation may be induced within the haptic device. In some examples, a system may include an optical element, and the desired surface deformation may be induced within the optical element.

In some examples, a non-transitory computer-readable medium includes one or more computer-executable instructions that, when executed by at least one processor of a computing device, cause the computing device to apply electrical signals between the first and second electrodes of a device, such as an electroactive device described herein, for example, to obtain a desired actuation of the device.

In some examples, a method of fabricating an anisotropic nanovoided polymer element includes depositing a nanovoided polymer deposited using a process including at least one of spin coating, printing, chemical vapor deposition, vapor coating, transfer of a prefabricated polymer layer, dipping, or spraying, and deforming the nanovoided polymer element by at least one of stretching, extruding, or pressing, to form the anisotropic nanovoided polymer element. An example method may further include forming a first electrode and a second electrode, for example, on opposed surfaces of the anisotropic nanovoided polymer element, so that at least part of the anisotropic nanovoided polymer element is located between the first electrode and the second electrode.

An example NVP includes anisotropic voids. Isotropic (spherical) voids may lead to non-uniform wall thicknesses and unstable buckling under compression. Anisotropic voids may also provide more uniform wall thicknesses and smoother and more reproducible electroactive response curves. Voids may be appreciably wider (e.g., in the plane of the electrodes) than tall, and the dimension ratio (which may also be termed an anisotropy ratio) may range from, for example, at least 1.5, such as at least 1.7, for example, at least 2, up to, for example, 10. Anisotropic voids facilitate compression in a direction normal to the plane of an electrode, for example, for anisotropic voids elongated in one or more directions parallel to the plane of the electrode. Similar approaches may be used with larger size scales, such as microscale voids. However, actuator response times may be longer with larger voids, particularly for closed void configurations, and may depend on the oxygen solubility of the polymer used.

Example polymers may include elastomers and may include, for example, silicone or acrylic polymers, and may be thermoset or otherwise polymerized. Example silicone polymers may include a poly(alkyl siloxane), such as a poly(dialkyl siloxane), such as poly(dimethyl siloxane) (PDMS). Manufacturing approaches may include extrusion, compression, stretching, phase separation, partial void collapse under solvent removal (e.g., to give disk-shaped voids), some combination thereof, and the like. Applications of such polymers include actuators, which may be relatively tolerant of random variations in void properties.

In some examples, a device includes a voided polymer element including an arrangement of voids; a first electrode; and a second electrode, where the voided polymer element is located at least in part between the first electrode and the second electrode. In these examples, the arrangement of voids may include anisotropic voids having a first dimension along a first direction greater than a second dimension along a second direction (e.g., along a second direction orthogonal to the first direction). The voids may have an anisotropy ratio determined by a ratio of a first dimension measured parallel to the first electrode divided by a second dimension measured perpendicular to the first electrode. Voids with an anisotropy ratio of one may be isotropic voids. In some examples, the anisotropy ratio may be in the range approximately 1.5-10 (e.g., in the range approximately 1.7-10, approximately 2-10, approximately 2-8, approximately 4-8, etc.). In some examples, ranges are inclusive and/or may be approximate. In some examples, the anisotropy ratio is at least 1.5. In other examples, the anisotropy ratio is at least 2. The anisotropy ratio may be determined an average, such as a median or mean, for a portion of the voided polymer element.

The arrangement of voids may be configured so that polymer wall thicknesses between neighboring voids are generally uniform. For example, a thickest portion of the polymer walls may be no greater than 50% larger than a thinnest portion. This ratio may be determined by sectioning the voided polymer element and determining an average (such as a median or mean) for a portion of the element. The portion may include, for example, approximately 20 voids. In some examples, a device includes a voided polymer element having an arrangement of voids therein; a first electrode; and a second electrode, where the voided polymer element is located at least in part between the first electrode and the second electrode and the arrangement of voids is configured so that polymer wall thicknesses between neighboring voids are generally uniform.

In some examples, a void shape may be designed to increase the uniformity of polymer walls. The arrangement of voids may include anisotropic voids that are configured to increase polymer wall thickness uniformity, with the anisotropic voids having a first dimension greater than a second dimension.

In some examples, the device may be (or include) an actuator. The device may further include a control circuit, where the control circuit is configured to apply an electrical potential between the first electrode and the second electrode. The device may be a spatially addressable actuator and may be a component of a haptic device. The device may be flexible; for example, the device may optionally have flexible substrates on which flexible electrodes are disposed, sandwiching a flexible voided polymer layer. Application of an electrical signal between the first electrode and the second electrode may induce a deformation of the voided polymer element, a pressure on a neighboring element, or movement of a neighboring element.

In some examples, the device is (or includes) an electrically controllable optical element, such as an electrically adjustable mirror or lens, and may be a component of a virtual reality or augmented reality system, a camera (such as a phone camera, video camera, self-contained camera), a projection system, telescope, binoculars, a portable electronic device, computer, or any other suitable electronic device or optical device, such as any autofocus system. The device may include one or more of a mirror, a lens, a prism, a grating, a phase plate, a diffuser, a holographic element, a beam splitter, a beam combiner, or an optical filter. The device may be (or include) a sensor. Examples include sensors (including touch sensors and any transducers) having greatly improved performance, particularly for relatively large mechanical inputs that induce significant mechanical compression (e.g., over 20%).

An example computer-implemented method includes applying an electrical signal between the first electrode and the second electrode of a device to obtain a desired surface deformation of the electroactive device. An example system includes at least one physical processor; physical memory including computer-executable instructions that, when executed by the physical processor, cause the physical processor to control application of electrical signals to a device to obtain an actuation of the device, and/or receive electrical signals from the device to obtain a sensor determination, for example, a touch detection or other sensor input. An example system includes a haptic device, a desired surface deformation being induced within the haptic device to provide haptic feedback to a user. An example system includes an optical element, with the desired surface deformation being induced within the optical element, and/or inducing a movement or deformation of an optical element such as a lens or mirror. An optical element may be a component of an augmented reality and/or virtual reality system, such as a headset, glasses, glove, or other AR/VR system or component thereof. An example non-transitory computer-readable medium includes one or more computer-executable instructions that, when executed by at least one processor of a computing device, cause the computing device to apply electrical signals to a device, for example, between the first and second electrodes of a device to obtain a desired actuation of the device, or a desired actuation of an optical element, or receive to receive sensor signals from a device.

In some embodiments, a method of fabricating an anisotropic voided polymer element includes depositing a voided polymer using a process including at least one of: spin coating, printing, chemical vapor deposition, vapor coating, transfer of a prefabricated polymer layer, dipping, or spraying; and deforming the voided polymer element by at least one of stretching, extruding, or pressing, to form the anisotropic voided polymer element. A fabrication method may further include forming electrodes, such as a first electrode and a second electrode on the anisotropic voided polymer element, so that at least part of the anisotropic voided polymer element is located between the first electrode and the second electrode.

In some examples, a method of fabricating an anisotropic voided polymer element includes depositing a voided polymer using a process including at least one of spin coating, printing (e.g., ink-jet printing), vapor deposition (e.g., chemical vapor deposition), vapor coating, transfer of a prefabricated polymer layer, dipping, or spraying; and deforming the voided polymer element by at least one of stretching, extruding, or pressing, to form the anisotropic voided polymer element. In some examples, a method may further include forming a first electrode and a second electrode on the anisotropic voided polymer element so that at least part of the anisotropic voided polymer element is located between the first electrode and the second electrode. In some examples, compositional variations may be introduced into a material using ink-jet printing. In some examples, compositional variations in a material layer may be used to introduce spatial variations in the electroactive properties of a nanovoided polymer formed from the material layer.

In some examples, a device, such as a polymer actuator, includes voids having generally non-spherical shapes. The void shapes may be configured to suppress buckling in the material and allow the material to be greatly compressed from its original shape in a controllable manner. The voids may be air-filled. A functional material may include a voided polymer where the voids are anisotropic in shape. Example anisotropic shapes include prolate shapes (e.g., elongated spheroids), elongate shapes such as cylinders (e.g., with rounded ends), oblate shapes (e.g., flattened spheroids), flattened shapes such as disks, and other geometric shapes. In some examples, a shorter dimension of a void shape may be aligned with the direction of compression of the NVP layer. The voids may be distributed periodically throughout the polymer layer, or in some examples may have no long-range periodicity. In some examples, a functional material is constrained to prevent expansion or contraction in one or more directions. In some examples, a voided polymer is used as the dielectric layer in an electrostatic actuator, such as an actuator that operates via mechanical actuation. The voided polymer material may include one or more polymer components, such as one or more silicone-based polymers, and/or one or more acrylic polymers. The voided polymer element may include an elastomer and/or a thermoset polymer. The voided polymer material may be actuated through compression or tension in one or more dimensions. For example, the voided polymer material may be actuated through compression or tension in two dimensions.

Examples include polymer devices, such as a polymer actuator. An example actuator includes a long thin block of material, which may include a polymer. A polymer actuator may compress in response to an applied electrical field. The degree of compression may be controlled by controlling the magnitude (e.g., the root mean square (rms) value) of the applied electric field. The actuator may take on a desired configuration and may exert a force on an adjacent surface. In some examples, the actuator may be used to modify an optical element (e.g., adjust the focal length of a flexible lens), or provide haptic feedback.

In example applications, several polymer actuators can be positioned along the rim of a pair of glasses including a flexible lens, such as a lens filled with a liquid. An electric field can be used to move the actuators so that they exert a force on the lens and change the focal point of the lens. Actuators may be configured to move an adjacent surface, for example, by distances up to 1 cm. The electrode separation may be of millimeter or sub-millimeter order to maintain reasonable voltage requirements for the actuator (e.g., less than 1 kV).

An actuator in compression may expand laterally, unless the actuator is laterally constrained, for example, by sidewalls. If the electroactive element of the actuator is constrained so that it cannot expand laterally, the force required to compress a solid electroactive element may be high, particularly if the electroactive element polymer material is close to incompressible. A NVP material may include many small pockets of gas (which may be referred to as voids). In some examples, voids may include a liquid, and the liquid may be removed by a process such as heating and/or reduce pressure. An NVP may be used as an electroactive element, and it may take less force to compress an NVP than a similarly sized solid polymer element. In some examples, compression of a gas (e.g., air) in the voids requires one or more orders of magnitude less force than that required to compress a solid block of material. Further, components of air (such as nitrogen and/or oxygen) may dissolve in the polymer matrix under compression, further reducing the force required to compress the NVP.

Voids may also help enable more precise control over how much the electroactive element deforms in response to a given electric field. In many applications, an ideal actuator may compress gradually and monotonically as the applied electric field (voltage) is increased, whereas a unstable actuator may show instability above a given voltage, for example, where the structure may rapidly collapse to a very compressed state. An unstable actuator may no longer have a predictable or reproducible voltage-actuation curve, which may be highly undesirable. The voltage-actuation curve may no longer be a monotonic function, and in some examples may show appreciable hysteresis. These effects may be reduced or substantially eliminated using a voided polymer element, in particular a nanovoided polymer element including anisotropic nanovoids.

In some examples, an actuator, such as an improved actuator including anisotropic nanovoids, may have a predictable and repeatable actuation response to a specified level of electric voltage. For example, the voltage-actuation response may be generally independent of the actuation history (e.g., whether actuation is increasing or decreasing). The actuation mechanism may survive many cycles of extending and retracting. The actuator response time can be sufficiently fast. This depends on applications, but example actuators may have a response time of less than 1 second, for example, from zero to maximum actuation, and in some examples, the response time may be less than 100 msec. In some examples, actuators including an NVP element having anisotropic nanovoids may achieve a maximum bulk compression of 50% or more.

In some embodiments, voided polymers can be created with spherical voids. In some manufacturing processes, spheres may be the relatively simplest shape to create. Arranging spherical voids for a high void fraction, configurations such as face-centered cubic (fcc) or body-centered cubic (bcc) may be used. However, using a spherical shape may lead to two problems in some examples. First, it may not be mathematically possible to make designs with a void fraction of over approximately 74%, as this is the packing limit for spherical voids (either in periodic or non-periodic arrangements). Designs having a void fraction close to the theoretical maximum have very thin walls in some locations and relatively thick walls elsewhere. Secondly, since the thickness of solid material between voids (wall thickness) can be highly variable with spherical voids, this encourages a buckling response as the material is compressed. Buckling of the material can lead to a rapid collapse that makes it difficult to control the actuation response with a high degree of precision.

Example actuators provide a mechanical component which moves in response to an input electrical signal. Anisotropic voids have spatial non-uniformity that differs in one direction from another direction. Anisotropy may be determined for orthogonal directions, for example, parallel to the plane of the electrodes and normal to the plane of the electrodes. Anisotropy may be determined for directions perpendicular to an electrical field and parallel to an electric field. For example, the mean thickness of an air void may be shorter in the height direction (perpendicular to an electrode) than in the length or width direction (parallel to the electrodes, for the case of parallel electrodes).

Actuation may be measured as a bulk compression. Compression may be measured in absolute units (e.g., a length unit) or as a fraction, for example, the fraction of the deformation relative to an original undeformed dimension of the actuator. For example, if the actuator is compressed and the thickness after compression is 70% of the original uncompressed thickness, then the bulk compression is 30%. Buckling is a usually undesirable behavior where part of a structure bends and folds over itself when a load is applied. Buckling is an instability that may trigger large deformations and a reduction in the load carrying capacity of the structure.

Voids may include a non-solid pocket in a solid polymer matrix. A void may be filled with air, an inert gas, or another gas (such as a high dielectric gas including polar molecules). Voids may include nanovoids, and examples may include nanovoided polymer elements (NVPs) with anisotropic voids. A nanovoid may have a diameter or other analogous dimension less than 1 micron, for example, in the range 1 nanometer-1 micrometer. The void fraction may represent the fraction of volume of the actuator (when in its original state with 0% bulk compression) occupied by voids, for example, by air or an inert gas. In some examples, voids may include microvoids, for example, with a void diameter or analogous dimension in the range of approximately 500 nm-500 microns, such as in the range 1 micron-100 microns.

Examples include an electroactive device, such as an actuator, with nanovoids having a non-spherical shape. In some examples, the voids have a form-fitting shape that results in more uniform wall thicknesses.

Anisotropic voids may be fabricated through processes such as pre-stretching or pre-tensioning a polymer element (such as an actuator or sensor element), for example, using an extrusion process, or a drawing process, or other process including a mechanical deformation such as stretching, pressing, or the like. Anisotropy can be locked in after stretching, for example, by further (e.g., complete) polymerization, cross-linking, curing, or other process. In some examples, an nanovoided polymer material may be extruded through a nozzle, which may have a generally slot-like opening, to form an anisotropic nanovoided polymer. A slot like opening may have a length in the range of approximately 1 mm-approximately 10 mm, and a width in the range of approximately 10 microns-1 mm. In some examples, an anisotropic nanovoided polymer may be extruded in the form of a fiber, and used in electroactive fabrics.

In some examples, shaped voids may be formed using shaped particles that may later be removed (e.g., shaped sacrificial particles), distortion of emulsions or lyotropic phases as a function of chemical composition, temperature, salt or other component concentration, flow rate, agitation, external fields (such as ultrasound, electrical, electromagnetic such as optical or UV, or magnetic fields). In some examples, voids may be extended arbitrarily along a direction, such as a direction parallel to an electrode, so that the voids are elongated shaped tubes with, for example, an anisotropic cross-section.

For actuator use, an electrical voltage may be applied between two electrodes, where at least a portion of the NVP is located between the two electrodes. Electrodes may be deposited onto the electroactive element. For example, first and second electrodes may be deposited so that at least part of the electroactive element lies between the electrodes. In some examples, a plurality of electrode pairs may be deposited. An electrode may be formed from an electrode material, such as a metal, alloy, or other conducting material such as graphite, graphene, carbon nanotubes, electrically conducting polymers, semiconductors, semi-metals, and the like. Suitable electrode materials include aluminum, indium, gallium, zinc, and other metals. Other conductive materials may be used including carbon nanotubes, graphene, transparent conductive oxides, and the like. The electrode coater may be a thermal evaporator, a sputtering system, or a spray coater.

An electrode layer may be very thin, for example, having an electrode layer thickness of between approximately 10 nm and approximately 50 nm. The electrode layer may be designed to allow healing of electrical breakdown in the EAP layer. A typical thickness of a self-healing aluminum electrode may be, for example, about 20 nm.

Example devices may include actuators, for example, having electrically-controllable compression, curvature, pressure on skin, texture, vibration, or other haptic function. Devices may be stacked to increase actuation. Example devices may be used to control optical elements, such as focal length or positional adjustments of lenses, mirrors, or other optical elements. Applications include improved autofocus and adaptive optics applications, such as in imaging devices. Applications also include wave-front correction of optical or other electromagnetic fields, for example, in projection systems. Examples include fine control actuators that can be combined with a coarser control actuator for extended actuation range. In some examples, actuators may be stacked to obtain enhanced actuation range. Examples also include sensors responsive to, for example, pressure (e.g., touch, acoustic signals, or vibration), temperature, and the like. Anisotropic voids may allow a more reproducible deformation under pressure and improved sensor operation. A sensor circuit may determine the magnitude of a mechanical input from a capacitance change. Example device structures described herein may also provide improved capacitance-deformation curves and improved sensor accuracy. Devices, such as sensors and actuators, may be curved, flexible, or otherwise conformal to an underlying substrate. Examples also include optical elements, such as gratings, holographic elements, lenses, mirrors, and the like. Electrodes may be transmissive or reflective. A device with reflective or transmissive electrodes may be an electrically-controllable optical element. In some examples, electrodes may be stretchable allowing bending. An example device may function both as an actuator and a touch sensor, and may also be reflective and/or optically transparent. Examples also include actuators configured to control a flexible lens (e.g., a liquid lens), flexible mirror, grating, prism, fiber, holographic element, or other optical element.

An electroactive device may include any device that either converts electrical energy to mechanical energy, or the reverse, or both, such as a sensor and/or an actuator. Electroactive devices may be used as haptic devices, optical elements, and other applications.

A nanovoided polymer may include a polymer material having voids therein. The voids may have a typical dimension of between 10 and 500 nm, such as between 50 and 200 nm. The voids may be closed cell (in which gas phase regions are isolated and surrounded by polymer) or open cell (in which gas phase regions are connected to each other).

In some examples, electrodes may be deposited on an intermediate layer supported by the voided polymer layer. An intermediate layer may include one or more planarization layers. A planarization layer may provide a surface of reduced surface roughness for the deposition of the electrodes. An intermediate layer (if used), and/or the NVP, may include one or more polymers, such as one or more of the following: acrylates; or halogenated polymers such as fluoropolymers, including polyvinylidene difluoride (PVDF, polytetrafluoroethylene), copolymers of PVDF including PVDF:TrFE (poly(polyvinylidene fluoride-trifluoroethylene), other fluorinated polyethylenes, other fluorinated polymers, other polymers, or blends or derivatives thereof. An intermediate layer (if used), and/or the NVP, may include one or more polymers, and may include particles (such as nanoparticles), for example, to increase the dielectric constant, and the particles may include inorganic particles such as one or more of the following: titanates (including barium titanate or barium strontium titanate (BaSrTiO₃)); oxides such as titanium dioxide (TiO₂), tantalum oxide (Ta₂O₃), aluminum oxide (Al₂O₃), or cerium oxide (CeO₂); other metal oxides such as other transition metal oxides, other non-metal oxides, or other compounds such as PbLaZrTiO₃, PbMgNbO₃+PbTiO₃. In some examples, mixtures of curable monomers with cured polymers may also be used. In some examples, a voided polymer layer may include one or more particles and/or polymers as discussed herein.

A controller may be configured to apply electrical signals to a plurality of electrodes of an electroactive device, for example, to obtain a desired surface deformation of an actuator and in some examples of an optical element including an actuator, such as a lens or mirror.

In some examples, a spatially addressable electroactive device includes a NVP element having a first and second surface, a first electrode supported by the NVP element, and a second electrode supported on the second surface. Example devices include a spatially addressable electroactive device such as an actuator, an optical element such as a transmissive or reflective optical element, or a sensor.

In some example devices, electrodes may be stretchable. In some example devices, an electrode may be disposed on a substrate, which may be a flexible and/or stretchable substrate. In some example devices, an NVP may support a plurality of electrodes (e.g., including the first electrode in examples above), and the second electrode may be a common electrode, such as a ground. In some examples, electrodes may include an array of electrical conductors of a pre-defined shape arranged in a pre-defined pattern.

In some examples, an electroactive device may be spatially addressable and may provide the ability to apply and/or read different signals at different spatial locations on the device. In some examples, multiplexing schemes can be used to apply electrical signals. In some examples, electrode pairs may be provided by the intersection of electrode stripes on each side of the NVP, for example, between orthogonal electrode stripes.

Example devices may be used in a range of applications. For example, a spatially addressed nanovoided polymer can be locally actuated. Actuation may be controlled by the size and arrangement of the electrodes at that location and the amount of voltage applied at those electrodes. Example devices can be used as an optical element, a touch sensor, a thermal sensor, a pressure sensor, or a haptic element in a wearable device.

A device may further include a control circuit configured to apply an electrical potential between the first electrode and the second electrode. A control circuit may be further configured to determine a physical deformation between the first electrode and the second electrode, for example, based on a capacitance determination. A device may be generally transparent, for example, including a nanovoided polymer that is generally transparent, and transparent electrodes (e.g., transparent conductive oxide electrodes such as tin oxide, indium tin oxide, and the like). A first electrode (and/or a second electrode) may be generally transparent, or in some examples may be generally reflective. A device may be flexible, and in some examples transparent and flexible.

An example device may include a spatially addressable actuator. Application of an electrical signal between the first electrode and the second electrode, and/or between other electrodes of the device, may induce a two-dimensional and/or three-dimensional conformational change of the nanovoided polymer element.

In some examples, the device may include an electrically controllable optical element, which may include one or more of a mirror, a lens, a prism, a grating, a phase place, a diffuser, a holographic element, a beam splitter, a beam combiner, or an optical filter. In some examples, the device may include a sensor, such as a touch sensor. An actuator may be controlled by an electrical potential between the first electrode and the second electrode, and a sensor responsive to a capacitance between the first electrode and the second electrode may be used to determine a degree of actuation (such as a displacement, relative displacement, or other deformation parameter).

In some examples, a system includes at least one physical processor and physical memory including computer-executable instructions that, when executed by the physical processor, cause the physical processor to control a deposition apparatus and/or stretching apparatus, for example, as described herein.

In some examples, a non-transitory computer-readable medium includes one or more computer-executable instructions that, when executed by at least one processor of a device, cause the device to deposit a material film, and/or process the material film using methods as described herein to form an anisotropic voided polymer, such as an anisotropic nanovoided polymer.

In some examples, a computer-implemented method includes application of electrical signals to a plurality of electrodes to obtain a desired surface deformation of an actuator, where the surface of the actuator supports a planarization layer on which the plurality of electrodes is disposed.

In some examples, a non-transitory computer-readable medium includes one or more computer-executable instructions that, when executed by at least one processor of a computing device, cause the computing device to control application of electrical signals to a plurality of electrodes of a device, such as an actuator to obtain a desired surface deformation of the device by application of electrical signals to electrodes. In some examples, signals of the same polarity may be applied to proximate electrodes to generate electrostatic repulsion and, for example, an increase in electrode separation.

In some examples, a computer-readable medium may include one or more computer-executable instructions that, when executed by at least one processor of a computing device, may cause the computing device to apply electrical signals to a plurality of electrodes of an electroactive device including an NVP element, for example, to obtain a desired surface deformation of the electroactive device. In some examples, a computer-readable medium may include one or more computer-executable instructions that, when executed by at least one processor of a computing device, may cause the computing device to receive and analyze electrical signals from a plurality of electrodes of an electroactive device including a NVP element, for example, to sense a surface deformation of the electroactive device, for example, to provide a sensor output representative of a surface deformation.

Example methods of fabricating NVP elements with anisotropic voids may include forming a material layer including voids and/or fluid droplets, and deforming the material layer to form anisotropic voids and/or droplets. In some examples, voids may be initially filled with one or more liquids, and liquid removal from the voids may induce partial void collapse into an anisotropic shape. For example, voids may initially be filled a plurality of liquid components, and preferential evaporation of at least one liquid component may induce void collapse.

Example approaches may also include applying a mechanical deformation to an NVP film, such as stretching in one or more directions, compression, or extrusion. Substrates may be used to apply mechanical deformations to an NVP element, and in some cases a substrate itself may be deformed to convey a deformation to an NVP element. Approaches may include using anisotropic particles (e.g., hollow nanoparticles), deformation of soft matter phases such as emulsions or lyotropic phases, application of electrical or magnetic fields, gas-diffusion expansion, or the use of IR, heat, or reduced pressure to remove liquid components. The NVP element may be partially polymerized before formation of anisotropic voids, with polymerization and/or cross-linking subsequently completed to lock in the anisotropic void shape(s). Spatial variations may be introduced using, for example, ink jet printing, or variations in radiation (e.g., UV) intensity.

In some examples, a device includes a nanovoided polymer (NVP) element, a first electrode; and a second electrode. The nanovoided polymer element may be located at least in part between the first electrode and the second electrode. In some examples, the nanovoided polymer element includes anisotropic voids. In some examples, the voids are configured so that a polymer wall thickness between neighboring voids is generally uniform. The device may be a spatially addressable electroactive device, such as an actuator or a sensor, and may include an optical element. The nanovoided polymer layer may include a polymer.

An example nanovoided polymer (NVP) includes anisotropic voids. Isotropic (spherical) voids may lead to non-uniform wall thicknesses and unstable buckling under compression. Anisotropic voids may provide more uniform wall thicknesses, and smoother and more reproducible electroactive response curves. Voids may be appreciably wider (e.g., in the plane of the electrodes) than tall, and the dimension ratio may range from, for example, at least 1.5, such as at least 1.7, for example, at least 2, up to, for example, 10. This anisotropy favors compression in a direction normal to the plane of the electrodes. Similar approaches may be used with larger size scales, such as microscale voids. However, actuator response times may be longer with larger voids, particularly for closed void configurations, and may depend on the oxygen solubility of the polymer used. Example polymers may be elastomers, may include, for example, silicone or acrylic polymers, and may be thermoset or otherwise polymerized. Manufacturing approaches may include extrusion, compression, stretching, phase separation, partial void collapse under solvent removal (e.g., to give disk-shaped voids), some combination thereof, and the like. Applications may include actuators, which may be relatively tolerant of random variations in void properties.

EXAMPLE EMBODIMENTS Example 1

A device including a first electrode, a second electrode, and an anisotropic nanovoided polymer including anisotropic nanovoids in a polymer matrix, where at least a portion of the anisotropic nanovoided polymer is located between the first electrode and the second electrode, and the anisotropic nanovoids are elongated along at least one direction parallel to the first electrode.

Example 2

The device of example 1, where the anisotropic nanovoids include oblate anisotropic voids.

Example 3

The device of any of examples 1-2, where the anisotropic nanovoids have an anisotropy ratio determined by a ratio of a first dimension measured along a first direction, and a second dimension measured perpendicular to the first direction.

Example 4

The device of any of examples 1-3, where the first direction is parallel to a plane of the first electrode.

Example 5

The device of any of examples 1-4, where the anisotropy ratio is between approximately 1.5 and approximately 10.

Example 6

The device of any of examples 1-4, where the anisotropy ratio is between approximately 2 and approximately 10.

Example 7

The device of any of examples 1-4, where the anisotropy ratio is between approximately 2 and approximately 8.

Example 8

The device of any of examples 1-4, where the anisotropy ratio is between approximately 4 and approximately 8.

Example 9

The device of any of examples 1-8, further including a control circuit, where the control circuit is configured to apply an electrical signal between the first electrode and the second electrode, and application of the electrical signal between the first electrode and the second electrode induces a deformation of the anisotropic nanovoided polymer.

Example 10

The device of any of examples 1-9, where the device includes an actuator.

Example 11

The device of any of examples 1-10, where the device includes a spatially addressable actuator, having a plurality of electrodes including the first electrode and the second electrode.

Example 12

The device of any of examples 1-11, where the device is an electrically controllable optical element.

Example 13

The device of any of examples 1-12, where the device includes one or more of a mirror, a lens, a prism, a grating, a phase plate, a diffuser, a holographic element, a beam splitter, a beam combiner, or an optical filter.

Example 14

The device of any of examples 1-13, further including a control circuit, where the control circuit is configured to detect an electrical signal between the first electrode and the second electrode, the electrical signal is generated between the first electrode and the second electrode by a deformation of the anisotropic nanovoided polymer, and the device is a sensor.

Example 15

A device including a nanovoided polymer element including an arrangement of nanovoids within a polymer matrix, a first electrode, and a second electrode, where the nanovoided polymer element is located at least in part between the first electrode and the second electrode, the arrangement of nanovoids include non-spherical nanovoids configured so that polymer wall thicknesses between neighboring nanovoids are generally uniform, and the device is a sensor or an actuator.

Example 16

The device of any of examples 1-15, where the nanovoids are anisotropic nanovoids, and the anisotropic nanovoids have an anisotropy ratio of at least 1.5, where the anisotropy ratio is a ratio of a first interior dimension along a first direction to a second interior dimension along a second direction, where the first direction is perpendicular to the second direction.

Example 17

A method of operating a device, the method including applying an electric field between a first electrode and a second electrode of the device, where the electric field induces a contraction of an anisotropic nanovoided polymer located, at least in part, between the first electrode and the second electrode, and mechanically coupling the contraction to a haptic output, where the device is a haptic device, the contraction of the anisotropic nanovoided polymer along the electric field includes a deformation of anisotropic nanovoids, and the anisotropic nanovoids are elongated in at least one direction perpendicular to the electric field.

Example 18

The method of example 17, where the anisotropic nanovoids are elongated within a plane perpendicular to the electric field.

Example 19

The method of any of examples 17-18, where the anisotropic nanovoids have a generally oblate spheroidal shape.

20. The method of any of examples 17-19, where the anisotropic nanovoids have an anisotropy ratio of at least 1.5 and the anisotropy ratio is a ratio of a first interior dimension perpendicular to the electric field to a second interior dimension parallel to the electric field.

FIG. 19 shows an example near-eye display system such as an augmented reality system. The system 1900 may include a near-eye display (NED) 1910 and a control system 1920, which may be communicatively coupled to each other. The near-eye display 1910 may include lenses 1912, electroactive devices 1914, displays 1916, and a sensor 1918. Control system 1920 may include a control element 1922, a force lookup table 1924, and augmented reality logic 1926.

Augmented reality logic 1926 may determine what virtual objects are to be displayed and real-world positions onto which the virtual objects are to be projected. Accordingly, augmented reality logic 1926 may generate an image stream 1928 that is displayed by displays 1916 in such a way that alignment of right- and left-side images displayed in displays 1916 results in ocular vergence toward a desired real-world position.

The control system 1922 may be configured to control one or more adjustable lenses, for example, a fluid element located within a near-eye display. Lens adjustment may be based on the desired perceived distance to a virtual object (this may, for example, include augmented reality image elements).

Control element 1922 may use the same positioning information determined by augmented reality logic 1926, in combination with force lookup table (LUT) 1924, to determine an amount of force to be applied by electroactive devices 1914 (e.g., actuators), as described herein, to lenses 1912. Electroactive devices 1914 may, responsive to control element 1922, apply appropriate forces to lenses 1912 to adjust the apparent accommodation distance of virtual images displayed in displays 1916 to match the apparent vergence distance of the virtual images, thereby reducing or eliminating vergence-accommodation conflict. Control element 1922 may be in communication with sensor 1918, which may measure a state of the adjustable lens. Based on data received from sensor 1918, the control element 1922 may adjust electroactive devices 1914 (e.g., as a closed-loop control system).

In some embodiments, display system 1900 may display multiple virtual objects at once and may determine which virtual object a user is viewing (or is likely to be viewing) to identify a virtual object for which to correct the apparent accommodation distance. For example, the system may include an eye-tracking system (not shown) that provides information to control element 1922 to enable control element 1922 to select the position of the relevant virtual object.

Additionally or alternatively, augmented reality logic 1926 may provide information about which virtual object is the most important and/or most likely to draw the attention of the user (e.g., based on spatial or temporal proximity, movement, and/or a semantic importance metric attached to the virtual object). In some embodiments, the augmented reality logic 1926 may identify multiple potentially important virtual objects and select an apparent accommodation distance that approximates the virtual distance of a group of the potentially important virtual objects.

Control system 1920 may represent any suitable hardware, software, or combination thereof for managing adjustments to adjustable lenses 1912. In some embodiments, control system 1920 may represent a system on a chip (SOC). As such, one or more portions of control system 1920 may include one or more hardware modules. Additionally or alternatively, one or more portions of control system 1920 may include one or more software modules that perform one or more of the tasks described herein when stored in the memory of a computing device and executed by a hardware processor of the computing device.

Control system 1920 may generally represent any suitable system for providing display data, augmented reality data, and/or augmented reality logic for a head-mounted display. In some embodiments, a control system 1920 may include a graphics processing unit (GPU) and/or any other type of hardware accelerator designed to optimize graphics processing.

Control system 1920 may be implemented in various types of systems, such as augmented reality glasses, which may further include one or more adjustable focus lenses coupled to a frame (e.g., using an eyewire). In some embodiments, a control system may be integrated into a frame of an eyewear device. Alternatively, all or a portion of control system may be in a system remote from the eyewear, and, for example, configured to control electroactive devices (e.g., actuators) in the eyewear via wired or wireless communication.

The control system, which in some examples may also be referred to as a controller, may control the operations of the light source and, in some cases, the optics system, which may include control of one or more fluid lenses. In some embodiments, the controller may be the graphics processing unit (GPU) of a display device. In some embodiments, the controller may include one or more different or additional processors. The operations performed by the controller may include taking content for display and dividing the content into discrete sections. The controller may instruct the light source to sequentially present the discrete sections using light emitters corresponding to a respective row in an image ultimately displayed to the user. The controller may instruct the optics system to adjust the light. For example, the controller may control the optics system to scan the presented discrete sections to different areas of a coupling element of the output waveguide. Accordingly, at the exit pupil of the output waveguide, each discrete portion may be presented in a different location. While each discrete section is presented at different times, the presentation and scanning of the discrete sections may occur fast enough such that a user's eye integrates the different sections into a single image or series of images. The controller may also provide scanning instructions to the light source that include an address corresponding to an individual source element of the light source and/or an electrical bias applied to the individual source element.

A controller may include an image processing unit. The controller, or component image processing unit, may include a general-purpose processor and/or one or more application-specific circuits that are dedicated to performing the features described herein. In one embodiment, a general-purpose processor may be coupled to a memory device to execute software instructions that cause the processor to perform certain processes described herein. In some embodiments, the image processing unit may include one or more circuits that are dedicated to performing certain features. The image processing unit may be a stand-alone unit that is separate from the controller and the driver circuit, but in some embodiments the image processing unit may be a sub-unit of the controller or the driver circuit. In other words, in those embodiments, the controller or the driver circuit performs various image processing procedures of the image processing unit. The image processing unit may also be referred to as an image processing circuit.

Ophthalmic applications of the devices described herein include spectacles with a flat front (or other curved) substrate and an adjustable eye-side concave or convex membrane surface. Applications include optics, and other applications of fluid lenses, including augmented reality or virtual reality headsets.

Embodiments of the present disclosure may include or be implemented in conjunction with various types of artificial reality systems. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, for example, a virtual reality, an augmented reality, a mixed reality, a hybrid reality, or some combination and/or derivative thereof. Artificial-reality content may include completely computer-generated content or computer-generated content combined with captured (e.g., real-world) content. The artificial-reality content may include video, audio, haptic feedback, or some combination thereof, any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional (3D) effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, for example, create content in an artificial reality and/or are otherwise used in (e.g., to perform activities in) an artificial reality.

Artificial-reality systems may be implemented in a variety of different form factors and configurations. Some artificial reality systems may be designed to work without near-eye displays (NEDs). Other artificial reality systems may include an NED that also provides visibility into the real world (e.g., augmented-reality system 2000 in FIG. 20) or that visually immerses a user in an artificial reality (e.g., virtual-reality system 2100 in FIG. 21). While some artificial-reality devices may be self-contained systems, other artificial-reality devices may communicate and/or coordinate with external devices to provide an artificial-reality experience to a user. Examples of such external devices include handheld controllers, mobile devices, desktop computers, devices worn by a user, devices worn by one or more other users, and/or any other suitable external system.

Turning to FIG. 20, augmented-reality system 2000 may include an eyewear device 2002 with a frame 2010 configured to hold a left display device 2015(A) and a right display device 2015(B) in front of a user's eyes. Display devices 2015(A) and 2015(B) may act together or independently to present an image or series of images to a user. While augmented-reality system 2000 includes two displays, embodiments of this disclosure may be implemented in augmented-reality systems with a single NED or more than two NEDs.

In some embodiments, augmented-reality system 2000 may include one or more sensors, such as sensor 2040. Sensor 2040 may generate measurement signals in response to motion of augmented-reality system 2000 and may be located on substantially any portion of frame 2010. Sensor 2040 may represent a position sensor, an inertial measurement unit (IMU), a depth camera assembly, a structured light emitter and/or detector, or any combination thereof. In some embodiments, augmented-reality system 2000 may or may not include sensor 2040 or may include more than one sensor. In embodiments in which sensor 2040 includes an IMU, the IMU may generate calibration data based on measurement signals from sensor 2040. Examples of sensor 2040 may include, without limitation, accelerometers, gyroscopes, magnetometers, other suitable types of sensors that detect motion, sensors used for error correction of the IMU, or some combination thereof.

Augmented-reality system 2000 may also include a microphone array with a plurality of acoustic transducers 2020(A)-2020(J), referred to collectively as acoustic transducers 2020. Acoustic transducers 2020 may be transducers that detect air pressure variations induced by sound waves. Each acoustic transducer 2020 may be configured to detect sound and convert the detected sound into an electronic format (e.g., an analog or digital format). The microphone array in FIG. 2 may include, for example, ten acoustic transducers: 2020(A) and 2020(B), which may be designed to be placed inside a corresponding ear of the user, acoustic transducers 2020(C), 2020(D), 2020(E), 2020(F), 2020(G), and 2020(H), which may be positioned at various locations on frame 2010, and/or acoustic transducers 2020(I) and 2020(J), which may be positioned on a corresponding neckband 2005.

In some embodiments, one or more of acoustic transducers 2020(A)-(F) may be used as output transducers (e.g., speakers). For example, acoustic transducers 2020(A) and/or 2020(B) may be earbuds or any other suitable type of headphone or speaker.

The configuration of acoustic transducers 2020 of the microphone array may vary. While augmented-reality system 2000 is shown in FIG. 20 as having ten acoustic transducers 2020, the number of acoustic transducers 2020 may be greater or less than ten. In some embodiments, using higher numbers of acoustic transducers 2020 may increase the amount of audio information collected and/or the sensitivity and accuracy of the audio information. In contrast, using a lower number of acoustic transducers 2020 may decrease the computing power required by an associated controller 2050 to process the collected audio information. In addition, the position of each acoustic transducer 2020 of the microphone array may vary. For example, the position of an acoustic transducer 2020 may include a defined position on the user, a defined coordinate on frame 2010, an orientation associated with each acoustic transducer 2020, or some combination thereof.

Acoustic transducers 2020(A) and 2020(B) may be positioned on different parts of the user's ear, such as behind the pinna, behind the tragus, and/or within the auricle or fossa. Or, there may be additional acoustic transducers 2020 on or surrounding the ear in addition to acoustic transducers 2020 inside the ear canal. Having an acoustic transducer 2020 positioned next to an ear canal of a user may enable the microphone array to collect information on how sounds arrive at the ear canal. By positioning at least two of acoustic transducers 2020 on either side of a user's head (e.g., as binaural microphones), augmented-reality device 2000 may simulate binaural hearing and capture a 3D stereo sound field around about a user's head. In some embodiments, acoustic transducers 2020(A) and 2020(B) may be connected to augmented-reality system 2000 via a wired connection 2030, and in other embodiments acoustic transducers 2020(A) and 2020(B) may be connected to augmented-reality system 2000 via a wireless connection (e.g., a Bluetooth connection). In still other embodiments, acoustic transducers 2020(A) and 2020(B) may not be used at all in conjunction with augmented-reality system 2000.

Acoustic transducers 2020 on frame 2010 may be positioned along the length of the temples, across the bridge, above or below display devices 2015(A) and 2015(B), or some combination thereof. Acoustic transducers 2020 may be oriented such that the microphone array is able to detect sounds in a wide range of directions surrounding the user wearing the augmented-reality system 2000. In some embodiments, an optimization process may be performed during manufacturing of augmented-reality system 2000 to determine relative positioning of each acoustic transducer 2020 in the microphone array.

In some examples, augmented-reality system 2000 may include or be connected to an external device (e.g., a paired device), such as neckband 2005. Neckband 2005 generally represents any type or form of paired device. Thus, the following discussion of neckband 2005 may also apply to various other paired devices, such as charging cases, smart watches, smart phones, wrist bands, other wearable devices, hand-held controllers, tablet computers, laptop computers, other external compute devices, etc.

As shown, neckband 2005 may be coupled to eyewear device 2002 via one or more connectors. The connectors may be wired or wireless and may include electrical and/or non-electrical (e.g., structural) components. In some cases, eyewear device 2002 and neckband 2005 may operate independently without any wired or wireless connection between them. While FIG. 20 illustrates the components of eyewear device 2002 and neckband 2005 in example locations on eyewear device 2002 and neckband 2005, the components may be located elsewhere and/or distributed differently on eyewear device 2002 and/or neckband 2005. In some embodiments, the components of eyewear device 2002 and neckband 2005 may be located on one or more additional peripheral devices paired with eyewear device 2002, neckband 2005, or some combination thereof.

Pairing external devices, such as neckband 2005, with augmented-reality eyewear devices may enable the eyewear devices to achieve the form factor of a pair of glasses while still providing sufficient battery and computation power for expanded capabilities. Some or all of the battery power, computational resources, and/or additional features of augmented-reality system 2000 may be provided by a paired device or shared between a paired device and an eyewear device, thus reducing the weight, heat profile, and form factor of the eyewear device overall while still retaining desired functionality. For example, neckband 2005 may allow components that would otherwise be included on an eyewear device to be included in neckband 2005 since users may tolerate a heavier weight load on their shoulders than they would tolerate on their heads. Neckband 2005 may also have a larger surface area over which to diffuse and disperse heat to the ambient environment. Thus, neckband 2005 may allow for greater battery and computation capacity than might otherwise have been possible on a stand-alone eyewear device. Since weight carried in neckband 2005 may be less invasive to a user than weight carried in eyewear device 2002, a user may tolerate wearing a lighter eyewear device and carrying or wearing the paired device for greater lengths of time than a user would tolerate wearing a heavy standalone eyewear device, thereby enabling users to more fully incorporate artificial reality environments into their day-to-day activities.

Neckband 2005 may be communicatively coupled with eyewear device 2002 and/or to other devices. These other devices may provide certain functions (e.g., tracking, localizing, depth mapping, processing, storage, etc.) to augmented-reality system 2000. In the embodiment of FIG. 20, neckband 2005 may include two acoustic transducers (e.g., 2020(I) and 2020(J)) that are part of the microphone array (or potentially form their own microphone subarray). Neckband 2005 may also include a controller 2025 and a power source 2035.

Acoustic transducers 2020(I) and 2020(J) of neckband 2005 may be configured to detect sound and convert the detected sound into an electronic format (analog or digital). In the embodiment of FIG. 20, acoustic transducers 2020(I) and 2020(J) may be positioned on neckband 2005, thereby increasing the distance between the neckband acoustic transducers 2020(I) and 2020(J) and other acoustic transducers 2020 positioned on eyewear device 2002. In some cases, increasing the distance between acoustic transducers 2020 of the microphone array may improve the accuracy of beamforming performed via the microphone array. For example, if a sound is detected by acoustic transducers 2020(C) and 2020(D) and the distance between acoustic transducers 2020(C) and 2020(D) is greater than, for example, the distance between acoustic transducers 2020(D) and 2020(E), the determined source location of the detected sound may be more accurate than if the sound had been detected by acoustic transducers 2020(D) and 2020(E).

Controller 2025 of neckband 2005 may process information generated by the sensors on neckband 2005 and/or augmented-reality system 2000. For example, controller 2025 may process information from the microphone array that describes sounds detected by the microphone array. For each detected sound, controller 2025 may perform a direction-of-arrival (DOA) estimation to estimate a direction from which the detected sound arrived at the microphone array. As the microphone array detects sounds, controller 2025 may populate an audio data set with the information. In embodiments in which augmented-reality system 2000 includes an inertial measurement unit, controller 2025 may compute all inertial and spatial calculations from the IMU located on eyewear device 2002. A connector may convey information between augmented-reality system 2000 and neckband 2005 and between augmented-reality system 2000 and controller 2025. The information may be in the form of optical data, electrical data, wireless data, or any other transmittable data form. Moving the processing of information generated by augmented-reality system 2000 to neckband 2005 may reduce weight and heat in eyewear device 2002, making it more comfortable to the user.

Power source 2035 in neckband 2005 may provide power to eyewear device 2002 and/or to neckband 2005. Power source 2035 may include, without limitation, lithium ion batteries, lithium-polymer batteries, primary lithium batteries, alkaline batteries, or any other form of power storage. In some cases, power source 2035 may be a wired power source. Including power source 2035 on neckband 2005 instead of on eyewear device 2002 may help better distribute the weight and heat generated by power source 2035.

As noted, some artificial reality systems may, instead of blending an artificial reality with actual reality, substantially replace one or more of a user's sensory perceptions of the real world with a virtual experience. One example of this type of system is a head-worn display system, such as virtual-reality system 2100 in FIG. 21, that mostly or completely covers a user's field of view. Virtual-reality system 2100 may include a front rigid body 2102 and a band 2104 shaped to fit around a user's head. Virtual-reality system 2100 may also include output audio transducers 2106(A) and 2106(B). Furthermore, while not shown in FIG. 21, front rigid body 2102 may include one or more electronic elements, including one or more electronic displays, one or more inertial measurement units (IMUS), one or more tracking emitters or detectors, and/or any other suitable device or system for creating an artificial reality experience.

Artificial reality systems may include a variety of types of visual feedback mechanisms. For example, display devices in augmented-reality system 2000 and/or virtual-reality system 2100 may include one or more liquid crystal displays (LCDs), light emitting diode (LED) displays, organic LED (OLED) displays digital light project (DLP) micro-displays, liquid crystal on silicon (LCoS) micro-displays, and/or any other suitable type of display screen. Artificial reality systems may include a single display screen for both eyes or may provide a display screen for each eye, which may allow for additional flexibility for varifocal adjustments or for correcting a user's refractive error. Some artificial reality systems may also include optical subsystems having one or more lenses (e.g., conventional concave or convex lenses, Fresnel lenses, adjustable liquid lenses, etc.) through which a user may view a display screen. These optical subsystems may serve a variety of purposes, including to collimate (e.g., make an object appear at a greater distance than its physical distance), to magnify (e.g., make an object appear larger than its actual size), and/or to relay (to, e.g., the viewer's eyes) light. These optical subsystems may be used in a non-pupil-forming architecture (such as a single lens configuration that directly collimates light but results in so-called pincushion distortion) and/or a pupil-forming architecture (such as a multi-lens configuration that produces so-called barrel distortion to nullify pincushion distortion).

In addition to or instead of using display screens, some artificial reality systems may include one or more projection systems. For example, display devices in augmented-reality system 2000 and/or virtual-reality system 2100 may include micro-LED projectors that project light (using, e.g., a waveguide) into display devices, such as clear combiner lenses that allow ambient light to pass through. The display devices may refract the projected light toward a user's pupil and may enable a user to simultaneously view both artificial reality content and the real world. The display devices may accomplish this using any of a variety of different optical components, including waveguides components (e.g., holographic, planar, diffractive, polarized, and/or reflective waveguide elements), light-manipulation surfaces and elements (such as diffractive, reflective, and refractive elements and gratings), coupling elements, etc. Artificial reality systems may also be configured with any other suitable type or form of image projection system, such as retinal projectors used in virtual retina displays.

Artificial reality systems may also include various types of computer vision components and subsystems. For example, augmented-reality system augmented-reality system 2000 and/or virtual-reality system 2100 may include one or more optical sensors, such as two-dimensional (2D) or 3D cameras, structured light transmitters and detectors, time-of-flight depth sensors, single-beam or sweeping laser rangefinders, 3D LiDAR sensors, and/or any other suitable type or form of optical sensor. An artificial reality system may process data from one or more of these sensors to identify a location of a user, to map the real world, to provide a user with context about real-world surroundings, and/or to perform a variety of other functions.

Artificial reality systems may also include one or more input and/or output audio transducers. Examples may include voice coil speakers, ribbon speakers, electrostatic speakers, piezoelectric speakers, bone conduction transducers, cartilage conduction transducers, tragus-vibration transducers, and/or any other suitable type or form of audio transducer. Similarly, input audio transducers may include condenser microphones, dynamic microphones, ribbon microphones, and/or any other type or form of input transducer. In some embodiments, a single transducer may be used for both audio input and audio output.

In some examples, artificial reality systems may include tactile (i.e., haptic) feedback systems, which may be incorporated into headwear, gloves, body suits, handheld controllers, environmental devices (e.g., chairs, floormats, etc.), and/or any other type of device or system. Haptic feedback systems may provide various types of cutaneous feedback, including vibration, force, traction, texture, and/or temperature. Haptic feedback systems may also provide various types of kinesthetic feedback, such as motion and compliance. Haptic feedback may be implemented using motors, piezoelectric actuators, fluidic systems, and/or a variety of other types of feedback mechanisms. Haptic feedback systems may be implemented independent of other artificial reality devices, within other artificial reality devices, and/or in conjunction with other artificial reality devices.

By providing haptic sensations, audible content, and/or visual content, artificial reality systems may create an entire virtual experience or enhance a user's real-world experience in a variety of contexts and environments. For instance, artificial reality systems may assist or extend a user's perception, memory, or cognition within a particular environment. Some systems may enhance a user's interactions with other people in the real world or may enable more immersive interactions with other people in a virtual world. Artificial reality systems may also be used for educational purposes (e.g., for teaching or training in schools, hospitals, government organizations, military organizations, business enterprises, etc.), entertainment purposes (e.g., for playing video games, listening to music, watching video content, etc.), and/or for accessibility purposes (e.g., as hearing aids, visuals aids, etc.). The embodiments disclosed herein may enable or enhance a user's artificial reality experience in one or more of these contexts and environments and/or in other contexts and environments.

As noted, artificial reality systems 2000 and 2100 may be used with a variety of other types of devices to provide a more compelling artificial reality experience. These devices may be haptic interfaces with transducers that provide haptic feedback and/or that collect haptic information about a user's interaction with an environment. The artificial-reality systems disclosed herein may include various types of haptic interfaces that detect or convey various types of haptic information, including tactile feedback (e.g., feedback that a user detects via nerves in the skin, which may also be referred to as cutaneous feedback) and/or kinesthetic feedback (e.g., feedback that a user detects via receptors located in muscles, joints, and/or tendons).

Haptic feedback may be provided by interfaces positioned within a user's environment (e.g., chairs, tables, floors, etc.) and/or interfaces on articles that may be worn or carried by a user (e.g., gloves, wristbands, etc.). As an example, FIG. 22 illustrates a vibrotactile system 2200 in the form of a wearable glove (haptic device 2210) and wristband (haptic device 2220). Haptic device 2210 and haptic device 2220 are shown as examples of wearable devices that include a flexible, wearable textile material 2230 that is shaped and configured for positioning against a user's hand and wrist, respectively. This disclosure also includes vibrotactile systems that may be shaped and configured for positioning against other human body parts, such as a finger, an arm, a head, a torso, a foot, or a leg. By way of example and not limitation, vibrotactile systems according to various embodiments of the present disclosure may also be in the form of a glove, a headband, an armband, a sleeve, a head covering, a sock, a shirt, or pants, among other possibilities. In some examples, the term “textile” may include any flexible, wearable material, including woven fabric, non-woven fabric, leather, cloth, a flexible polymer material, composite materials, etc.

One or more vibrotactile devices 2240 may be positioned at least partially within one or more corresponding pockets formed in textile material 2230 of vibrotactile system 2200. Vibrotactile devices 2240 may be positioned in locations to provide a vibrating sensation (e.g., haptic feedback) to a user of vibrotactile system 2200. For example, vibrotactile devices 2240 may be positioned against the user's finger(s), thumb, or wrist, as shown in FIG. 22. Vibrotactile devices 2240 may, in some examples, be sufficiently flexible to conform to or bend with the user's corresponding body part(s).

A power source 2250 (e.g., a battery) for applying a voltage to the vibrotactile devices 2240 for activation thereof may be electrically coupled to vibrotactile devices 2240, such as via conductive wiring 2252. In some examples, each of vibrotactile devices 2240 may be independently electrically coupled to power source 2250 for individual activation. In some embodiments, a processor 2260 may be operatively coupled to power source 2250 and configured (e.g., programmed) to control activation of vibrotactile devices 2240.

Vibrotactile system 2200 may be implemented in a variety of ways. In some examples, vibrotactile system 2200 may be a standalone system with integral subsystems and components for operation independent of other devices and systems. As another example, vibrotactile system 2200 may be configured for interaction with another device or system 2270. For example, vibrotactile system 2200 may, in some examples, include a communications interface 2280 for receiving and/or sending signals to the other device or system 2270. The other device or system 2270 may be a mobile device, a gaming console, an artificial reality (e.g., virtual reality, augmented reality, mixed reality) device, a personal computer, a tablet computer, a network device (e.g., a modem, a router, etc.), a handheld controller, etc. Communications interface 2280 may enable communications between vibrotactile system 2200 and the other device or system 2270 via a wireless (e.g., Wi-Fi, Bluetooth, cellular, radio, etc.) link or a wired link. If present, communications interface 2280 may be in communication with processor 2260, such as to provide a signal to processor 2260 to activate or deactivate one or more of the vibrotactile devices 2240.

Vibrotactile system 2200 may optionally include other subsystems and components, such as touch-sensitive pads 2290, pressure sensors, motion sensors, position sensors, lighting elements, and/or user interface elements (e.g., an on/off button, a vibration control element, etc.). During use, vibrotactile devices 2240 may be configured to be activated for a variety of different reasons, such as in response to the user's interaction with user interface elements, a signal from the motion or position sensors, a signal from the touch-sensitive pads 2290, a signal from the pressure sensors, a signal from the other device or system 2270, etc.

Although power source 2250, processor 2260, and communications interface 2280 are illustrated in FIG. 22 as being positioned in haptic device 2220, the present disclosure is not so limited. For example, one or more of power source 2250, processor 2260, or communications interface 2280 may be positioned within haptic device 2210 or within another wearable textile.

Haptic wearables, such as those shown in and described in connection with FIG. 22, may be implemented in a variety of types of artificial-reality systems and environments. FIG. 23 shows an example artificial reality environment 2300 including one head-mounted virtual-reality display and two haptic devices (i.e., gloves), and in other embodiments any number and/or combination of these components and other components may be included in an artificial reality system. For example, in some embodiments there may be multiple head-mounted displays each having an associated haptic device, with each head-mounted display and each haptic device communicating with the same console, portable computing device, or other computing system.

Head-mounted display 2302 generally represents any type or form of virtual-reality system, such as virtual-reality system 2100 in FIG. 21. Haptic device 2304 generally represents any type or form of wearable device, worn by a user of an artificial reality system, that provides haptic feedback to the user to give the user the perception that he or she is physically engaging with a virtual object. In some embodiments, haptic device 2304 may provide haptic feedback by applying vibration, motion, and/or force to the user. For example, haptic device 2304 may limit or augment a user's movement. To give a specific example, haptic device 2304 may limit a user's hand from moving forward so that the user has the perception that his or her hand has come in physical contact with a virtual wall. In this specific example, one or more actuators within the haptic advice may achieve the physical-movement restriction by pumping fluid into an inflatable bladder of the haptic device. In some examples, a user may also use haptic device 2304 to send action requests to a console. Examples of action requests include, without limitation, requests to start an application and/or end the application and/or requests to perform a particular action within the application.

While haptic interfaces may be used with virtual-reality systems, as shown in FIG. 23, haptic interfaces may also be used with augmented-reality systems, as shown in FIG. 24. FIG. 24 is a perspective view of a user 2410 interacting with an augmented-reality system 2400. In this example, user 2410 may wear a pair of augmented-reality glasses 2420 that may have one or more displays 2422 and that are paired with a haptic device 2430. In this example, haptic device 2430 may be a wristband that includes a plurality of band elements 2432 and a tensioning mechanism 2434 that connects band elements 2432 to one another.

One or more of band elements 2432 may include any type or form of actuator suitable for providing haptic feedback. For example, one or more of band elements 2432 may be configured to provide one or more of various types of cutaneous feedback, including vibration, force, traction, texture, and/or temperature. To provide such feedback, band elements 2432 may include one or more of various types of actuators. In one example, each of band elements 2432 may include a vibrotactor (e.g., a vibrotactile actuator) configured to vibrate in unison or independently to provide one or more of various types of haptic sensations to a user. Alternatively, only a single band element or a subset of band elements may include vibrotactors.

Haptic devices 2210, 2220, 2304, and 2430 may include any suitable number and/or type of haptic transducer, sensor, and/or feedback mechanism. For example, haptic devices 2210, 2220, 2304, and 2430 may include one or more mechanical transducers, piezoelectric transducers, and/or fluidic transducers. Haptic devices 2210, 2220, 2304, and 2430 may also include various combinations of different types and forms of transducers that work together or independently to enhance a user's artificial-reality experience. In one example, each of band elements 2432 of haptic device 2430 may include a vibrotactor (e.g., a vibrotactile actuator) configured to vibrate in unison or independently to provide one or more of various types of haptic sensations to a user.

As detailed above, the computing devices and systems described and/or illustrated herein broadly represent any type or form of computing device or system capable of executing computer-readable instructions, such as those contained within the modules described herein. In their most basic configuration, these computing device(s) may each include at least one memory device and at least one physical processor.

In some examples, the term “memory device” generally refers to any type or form of volatile or non-volatile storage device or medium capable of storing data and/or computer-readable instructions. In one example, a memory device may store, load, and/or maintain one or more of the modules described herein. Examples of memory devices include, without limitation, Random Access Memory (RAM), Read Only Memory (ROM), flash memory, Hard Disk Drives (HDDs), Solid-State Drives (SSDs), optical disk drives, caches, variations or combinations of one or more of the same, or any other suitable storage memory.

In some examples, the term “physical processor” generally refers to any type or form of hardware-implemented processing unit capable of interpreting and/or executing computer-readable instructions. In one example, a physical processor may access and/or modify one or more modules stored in the above-described memory device. Examples of physical processors include, without limitation, microprocessors, microcontrollers, Central Processing Units (CPUs), Field-Programmable Gate Arrays (FPGAs) that implement softcore processors, Application-Specific Integrated Circuits (ASICs), portions of one or more of the same, variations or combinations of one or more of the same, or any other suitable physical processor.

Although illustrated as separate elements, the modules described and/or illustrated herein may represent portions of a single module or application. In addition, in certain embodiments one or more of these modules may represent one or more software applications or programs that, when executed by a computing device, may cause the computing device to perform one or more tasks. For example, one or more of the modules described and/or illustrated herein may represent modules stored and configured to run on one or more of the computing devices or systems described and/or illustrated herein. One or more of these modules may also represent all or portions of one or more special-purpose computers configured to perform one or more tasks.

In addition, one or more of the modules described herein may transform data, physical devices, and/or representations of physical devices from one form to another. For example, one or more of the modules recited herein may receive [data] to be transformed, transform the [data], output a result of the transformation to [perform a function], use the result of the transformation to [perform a function], and store the result of the transformation to [perform a function]. Additionally or alternatively, one or more of the modules recited herein may transform a processor, volatile memory, non-volatile memory, and/or any other portion of a physical computing device from one form to another by executing on the computing device, storing data on the computing device, and/or otherwise interacting with the computing device.

In some embodiments, the term “computer-readable medium” generally refers to any form of device, carrier, or medium capable of storing or carrying computer-readable instructions. Examples of computer-readable media include, without limitation, transmission-type media, such as carrier waves, and non-transitory-type media, such as magnetic-storage media (e.g., hard disk drives, tape drives, and floppy disks), optical-storage media (e.g., Compact Disks (CDs), Digital Video Disks (DVDs), and BLU-RAY disks), electronic-storage media (e.g., solid-state drives and flash media), and other distribution systems.

The process parameters and sequence of the steps described and/or illustrated herein are given by way of example only and can be varied as desired. For example, while the steps illustrated and/or described herein may be shown or discussed in a particular order, these steps do not necessarily need to be performed in the order illustrated or discussed. The various exemplary methods described and/or illustrated herein may also omit one or more of the steps described or illustrated herein or include additional steps in addition to those disclosed.

The preceding description has been provided to enable others skilled in the art to best utilize various aspects of the exemplary embodiments disclosed herein. This exemplary description is not intended to be exhaustive or to be limited to any precise form disclosed. Many modifications and variations are possible without departing from the spirit and scope of the present disclosure. The embodiments disclosed herein should be considered in all respects illustrative and not restrictive. Reference should be made to the appended claims and their equivalents in determining the scope of the present disclosure.

U.S. Provisional Application No. 62/777,825, filed Dec. 11, 2018, is incorporated, in its entirety, by this reference.

Unless otherwise noted, the terms “connected to” and “coupled to” (and their derivatives), as used in the specification and claims, are to be construed as permitting both direct and indirect (i.e., via other elements or components) connection. In addition, the terms “a” or “an,” as used in the specification and claims, are to be construed as meaning “at least one of.” Finally, for ease of use, the terms “including” and “having” (and their derivatives), as used in the specification and claims, are interchangeable with and have the same meaning as the word “comprising.”

Features from any of the embodiments described herein may be used in combination with one another in accordance with the general principles described herein. These and other embodiments, features, and advantages will be more fully understood upon reading the following detailed description in conjunction with the accompanying drawings and claims. 

What is claimed is:
 1. A device, comprising: a first electrode; a second electrode; and an anisotropic nanovoided polymer comprising anisotropic nanovoids in a polymer matrix, wherein: at least a portion of the anisotropic nanovoided polymer is located between the first electrode and the second electrode, and the anisotropic nanovoids are elongated along at least one direction parallel to the first electrode.
 2. The device of claim 1, wherein the anisotropic nanovoids comprise oblate anisotropic voids.
 3. The device of claim 1, wherein the anisotropic nanovoids have an anisotropy ratio determined by a ratio of a first dimension measured along a first direction, and a second dimension measured perpendicular to the first direction.
 4. The device of claim 3, wherein the first direction is parallel to a plane of the first electrode.
 5. The device of claim 4, wherein the anisotropy ratio is between approximately 1.5 and approximately
 10. 6. The device of claim 4, wherein the anisotropy ratio is between approximately 2 and approximately
 10. 7. The device of claim 4, wherein the anisotropy ratio is between approximately 2 and approximately
 8. 8. The device of claim 4, wherein the anisotropy ratio is between approximately 4 and approximately
 8. 9. The device of claim 1, further comprising a control circuit, wherein the control circuit is configured to apply an electrical signal between the first electrode and the second electrode, and application of the electrical signal between the first electrode and the second electrode induces a deformation of the anisotropic nanovoided polymer.
 10. The device of claim 9, wherein the device is an actuator.
 11. The device of claim 9, wherein the device is a spatially addressable actuator, having a plurality of electrodes including the first electrode and the second electrode.
 12. The device of claim 1, wherein the device is an electrically controllable optical element.
 13. The device of claim 12, wherein the device comprises one or more of a mirror, a lens, a prism, a grating, a phase plate, a diffuser, a holographic element, a beam splitter, a beam combiner, or an optical filter.
 14. The device of claim 1, further comprising a control circuit, wherein the control circuit is configured to detect an electrical signal between the first electrode and the second electrode, the electrical signal is generated between the first electrode and the second electrode by a deformation of the anisotropic nanovoided polymer, and the device is a sensor.
 15. A device comprising: a nanovoided polymer element comprising an arrangement of nanovoids within a polymer matrix; a first electrode; and a second electrode, wherein the nanovoided polymer element is located at least in part between the first electrode and the second electrode, the arrangement of nanovoids include non-spherical nanovoids configured so that polymer wall thicknesses between neighboring nanovoids are generally uniform, and the device is a sensor or an actuator.
 16. The device of claim 15, wherein the nanovoids are anisotropic nanovoids, and the anisotropic nanovoids have an anisotropy ratio of at least 1.5, wherein the anisotropy ratio is a ratio of a first interior dimension along a first direction to a second interior dimension along a second direction, wherein the first direction is perpendicular to the second direction.
 17. A method of operating a device, the method comprising: applying an electric field between a first electrode and a second electrode of the device, wherein the electric field induces a contraction of an anisotropic nanovoided polymer located, at least in part, between the first electrode and the second electrode; and mechanically coupling the contraction to a haptic output, wherein the device is a haptic device, the contraction of the anisotropic nanovoided polymer along the electric field includes a deformation of anisotropic nanovoids, and the anisotropic nanovoids are elongated in at least one direction perpendicular to the electric field.
 18. The method of claim 17, wherein the anisotropic nanovoids are elongated within a plane perpendicular to the electric field.
 19. The method of claim 18, wherein the anisotropic nanovoids have a generally oblate spheroidal shape.
 20. The method of claim 17, wherein the anisotropic nanovoids have an anisotropy ratio of at least 1.5 and the anisotropy ratio is a ratio of a first interior dimension perpendicular to the electric field to a second interior dimension parallel to the electric field. 